#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }

////////////////////////////////////////////////////////////////////////////////
template <unsigned M_> struct ModInt {
  static constexpr unsigned M = M_;
  unsigned x;
  constexpr ModInt() : x(0U) {}
  constexpr ModInt(unsigned x_) : x(x_ % M) {}
  constexpr ModInt(unsigned long long x_) : x(x_ % M) {}
  constexpr ModInt(int x_) : x(((x_ %= static_cast<int>(M)) < 0) ? (x_ + static_cast<int>(M)) : x_) {}
  constexpr ModInt(long long x_) : x(((x_ %= static_cast<long long>(M)) < 0) ? (x_ + static_cast<long long>(M)) : x_) {}
  ModInt &operator+=(const ModInt &a) { x = ((x += a.x) >= M) ? (x - M) : x; return *this; }
  ModInt &operator-=(const ModInt &a) { x = ((x -= a.x) >= M) ? (x + M) : x; return *this; }
  ModInt &operator*=(const ModInt &a) { x = (static_cast<unsigned long long>(x) * a.x) % M; return *this; }
  ModInt &operator/=(const ModInt &a) { return (*this *= a.inv()); }
  ModInt pow(long long e) const {
    if (e < 0) return inv().pow(-e);
    ModInt a = *this, b = 1U; for (; e; e >>= 1) { if (e & 1) b *= a; a *= a; } return b;
  }
  ModInt inv() const {
    unsigned a = M, b = x; int y = 0, z = 1;
    for (; b; ) { const unsigned q = a / b; const unsigned c = a - q * b; a = b; b = c; const int w = y - static_cast<int>(q) * z; y = z; z = w; }
    assert(a == 1U); return ModInt(y);
  }
  ModInt operator+() const { return *this; }
  ModInt operator-() const { ModInt a; a.x = x ? (M - x) : 0U; return a; }
  ModInt operator+(const ModInt &a) const { return (ModInt(*this) += a); }
  ModInt operator-(const ModInt &a) const { return (ModInt(*this) -= a); }
  ModInt operator*(const ModInt &a) const { return (ModInt(*this) *= a); }
  ModInt operator/(const ModInt &a) const { return (ModInt(*this) /= a); }
  template <class T> friend ModInt operator+(T a, const ModInt &b) { return (ModInt(a) += b); }
  template <class T> friend ModInt operator-(T a, const ModInt &b) { return (ModInt(a) -= b); }
  template <class T> friend ModInt operator*(T a, const ModInt &b) { return (ModInt(a) *= b); }
  template <class T> friend ModInt operator/(T a, const ModInt &b) { return (ModInt(a) /= b); }
  explicit operator bool() const { return x; }
  bool operator==(const ModInt &a) const { return (x == a.x); }
  bool operator!=(const ModInt &a) const { return (x != a.x); }
  friend std::ostream &operator<<(std::ostream &os, const ModInt &a) { return os << a.x; }
};
////////////////////////////////////////////////////////////////////////////////

////////////////////////////////////////////////////////////////////////////////
constexpr unsigned MO = 998244353U;
constexpr unsigned MO2 = 2U * MO;
constexpr int FFT_MAX = 23;
using Mint = ModInt<MO>;
constexpr Mint FFT_ROOTS[FFT_MAX + 1] = {1U, 998244352U, 911660635U, 372528824U, 929031873U, 452798380U, 922799308U, 781712469U, 476477967U, 166035806U, 258648936U, 584193783U, 63912897U, 350007156U, 666702199U, 968855178U, 629671588U, 24514907U, 996173970U, 363395222U, 565042129U, 733596141U, 267099868U, 15311432U};
constexpr Mint INV_FFT_ROOTS[FFT_MAX + 1] = {1U, 998244352U, 86583718U, 509520358U, 337190230U, 87557064U, 609441965U, 135236158U, 304459705U, 685443576U, 381598368U, 335559352U, 129292727U, 358024708U, 814576206U, 708402881U, 283043518U, 3707709U, 121392023U, 704923114U, 950391366U, 428961804U, 382752275U, 469870224U};
constexpr Mint FFT_RATIOS[FFT_MAX] = {911660635U, 509520358U, 369330050U, 332049552U, 983190778U, 123842337U, 238493703U, 975955924U, 603855026U, 856644456U, 131300601U, 842657263U, 730768835U, 942482514U, 806263778U, 151565301U, 510815449U, 503497456U, 743006876U, 741047443U, 56250497U, 867605899U};
constexpr Mint INV_FFT_RATIOS[FFT_MAX] = {86583718U, 372528824U, 373294451U, 645684063U, 112220581U, 692852209U, 155456985U, 797128860U, 90816748U, 860285882U, 927414960U, 354738543U, 109331171U, 293255632U, 535113200U, 308540755U, 121186627U, 608385704U, 438932459U, 359477183U, 824071951U, 103369235U};

// as[rev(i)] <- \sum_j \zeta^(ij) as[j]
void fft(Mint *as, int n) {
  assert(!(n & (n - 1))); assert(1 <= n); assert(n <= 1 << FFT_MAX);
  int m = n;
  if (m >>= 1) {
    for (int i = 0; i < m; ++i) {
      const unsigned x = as[i + m].x;  // < MO
      as[i + m].x = as[i].x + MO - x;  // < 2 MO
      as[i].x += x;  // < 2 MO
    }
  }
  if (m >>= 1) {
    Mint prod = 1U;
    for (int h = 0, i0 = 0; i0 < n; i0 += (m << 1)) {
      for (int i = i0; i < i0 + m; ++i) {
        const unsigned x = (prod * as[i + m]).x;  // < MO
        as[i + m].x = as[i].x + MO - x;  // < 3 MO
        as[i].x += x;  // < 3 MO
      }
      prod *= FFT_RATIOS[__builtin_ctz(++h)];
    }
  }
  for (; m; ) {
    if (m >>= 1) {
      Mint prod = 1U;
      for (int h = 0, i0 = 0; i0 < n; i0 += (m << 1)) {
        for (int i = i0; i < i0 + m; ++i) {
          const unsigned x = (prod * as[i + m]).x;  // < MO
          as[i + m].x = as[i].x + MO - x;  // < 4 MO
          as[i].x += x;  // < 4 MO
        }
        prod *= FFT_RATIOS[__builtin_ctz(++h)];
      }
    }
    if (m >>= 1) {
      Mint prod = 1U;
      for (int h = 0, i0 = 0; i0 < n; i0 += (m << 1)) {
        for (int i = i0; i < i0 + m; ++i) {
          const unsigned x = (prod * as[i + m]).x;  // < MO
          as[i].x = (as[i].x >= MO2) ? (as[i].x - MO2) : as[i].x;  // < 2 MO
          as[i + m].x = as[i].x + MO - x;  // < 3 MO
          as[i].x += x;  // < 3 MO
        }
        prod *= FFT_RATIOS[__builtin_ctz(++h)];
      }
    }
  }
  for (int i = 0; i < n; ++i) {
    as[i].x = (as[i].x >= MO2) ? (as[i].x - MO2) : as[i].x;  // < 2 MO
    as[i].x = (as[i].x >= MO) ? (as[i].x - MO) : as[i].x;  // < MO
  }
}

// as[i] <- (1/n) \sum_j \zeta^(-ij) as[rev(j)]
void invFft(Mint *as, int n) {
  assert(!(n & (n - 1))); assert(1 <= n); assert(n <= 1 << FFT_MAX);
  int m = 1;
  if (m < n >> 1) {
    Mint prod = 1U;
    for (int h = 0, i0 = 0; i0 < n; i0 += (m << 1)) {
      for (int i = i0; i < i0 + m; ++i) {
        const unsigned long long y = as[i].x + MO - as[i + m].x;  // < 2 MO
        as[i].x += as[i + m].x;  // < 2 MO
        as[i + m].x = (prod.x * y) % MO;  // < MO
      }
      prod *= INV_FFT_RATIOS[__builtin_ctz(++h)];
    }
    m <<= 1;
  }
  for (; m < n >> 1; m <<= 1) {
    Mint prod = 1U;
    for (int h = 0, i0 = 0; i0 < n; i0 += (m << 1)) {
      for (int i = i0; i < i0 + (m >> 1); ++i) {
        const unsigned long long y = as[i].x + MO2 - as[i + m].x;  // < 4 MO
        as[i].x += as[i + m].x;  // < 4 MO
        as[i].x = (as[i].x >= MO2) ? (as[i].x - MO2) : as[i].x;  // < 2 MO
        as[i + m].x = (prod.x * y) % MO;  // < MO
      }
      for (int i = i0 + (m >> 1); i < i0 + m; ++i) {
        const unsigned long long y = as[i].x + MO - as[i + m].x;  // < 2 MO
        as[i].x += as[i + m].x;  // < 2 MO
        as[i + m].x = (prod.x * y) % MO;  // < MO
      }
      prod *= INV_FFT_RATIOS[__builtin_ctz(++h)];
    }
  }
  if (m < n) {
    for (int i = 0; i < m; ++i) {
      const unsigned y = as[i].x + MO2 - as[i + m].x;  // < 4 MO
      as[i].x += as[i + m].x;  // < 4 MO
      as[i + m].x = y;  // < 4 MO
    }
  }
  const Mint invN = Mint(n).inv();
  for (int i = 0; i < n; ++i) {
    as[i] *= invN;
  }
}

void fft(vector<Mint> &as) {
  fft(as.data(), as.size());
}
void invFft(vector<Mint> &as) {
  invFft(as.data(), as.size());
}

vector<Mint> convolve(vector<Mint> as, vector<Mint> bs) {
  if (as.empty() || bs.empty()) return {};
  const int len = as.size() + bs.size() - 1;
  int n = 1;
  for (; n < len; n <<= 1) {}
  as.resize(n); fft(as);
  bs.resize(n); fft(bs);
  for (int i = 0; i < n; ++i) as[i] *= bs[i];
  invFft(as);
  as.resize(len);
  return as;
}
vector<Mint> square(vector<Mint> as) {
  if (as.empty()) return {};
  const int len = as.size() + as.size() - 1;
  int n = 1;
  for (; n < len; n <<= 1) {}
  as.resize(n); fft(as);
  for (int i = 0; i < n; ++i) as[i] *= as[i];
  invFft(as);
  as.resize(len);
  return as;
}
////////////////////////////////////////////////////////////////////////////////

/*
  [0, n] * [0, n - m + 1]
  
  [ a[0]                     ]
  [ ...    a[0]              ]
  [ a[m-1] ...               ]
  [        a[m-1]            ]
  [               ...        ]
  [                   a[0]   ]
  [                   ...    ]
  [                   a[m-1] ]
  
  [x^j] (rev(a) b)  m - 1 <= j <= n - 1
*/
vector<Mint> middle(vector<Mint> as, vector<Mint> bs) {
  const int m = as.size();
  const int n = bs.size();
  assert(m <= n);
  int nn = 1;
  for (; nn < n; nn <<= 1) {}
  reverse(as.begin(), as.end());
  as.resize(nn, 0);
  fft(as);
  bs.resize(nn, 0);
  fft(bs);
  for (int i = 0; i < nn; ++i) {
    bs[i] *= as[i];
  }
  invFft(bs);
  bs.resize(n);
  bs.erase(bs.begin(), bs.begin() + (m - 1));
  return bs;
}

////////////////////////////////////////////////////////////////////////////////
// SA-IS
//   String: string, vector<int>, vector<long long>
//   if sigma <= n,  O(n) time, O(n) space
//   if sigma >  n,  O(n log n) time, O(n) space
template <class String> vector<int> suffixArrayRec(const String &as) {
  const int n = as.size();
  if (n == 0) return {};
  const auto minmaxA = minmax_element(as.begin(), as.end());
  const auto minA = *minmaxA.first, maxA = *minmaxA.second;
  if (static_cast<unsigned long long>(maxA) - minA >=
      static_cast<unsigned long long>(n)) {
    vector<int> us(n);
    for (int u = 0; u < n; ++u) us[u] = u;
    std::sort(us.begin(), us.end(), [&](int u, int v) -> bool {
      return (as[u] < as[v]);
    });
    int b = 0;
    vector<int> bs(n, 0);
    for (int i = 1; i < n; ++i) {
      if (as[us[i - 1]] != as[us[i]]) ++b;
      bs[us[i]] = b;
    }
    return suffixArrayRec(bs);
  }
  const int sigma = maxA - minA + 1;
  vector<int> pt(sigma + 1, 0), poss(sigma);
  for (int u = 0; u < n; ++u) ++pt[as[u] - minA + 1];
  for (int a = 0; a < sigma; ++a) pt[a + 1] += pt[a];
  // cmp[u] := (as[u, n) < as[u + 1, n))
  vector<bool> cmp(n);
  cmp[n - 1] = false;
  for (int u = n - 1; --u >= 0; ) {
    cmp[u] = (as[u] != as[u + 1]) ? (as[u] < as[u + 1]) : cmp[u + 1];
  }
  // ><,  nn - id (0 <= id < n)
  int nn = 0;
  vector<int> ids(n, 0);
  int last = n;
  vector<int> nxt(n, 0);
  // put ><, from the tail of each bucket
  vector<int> us(n, 0);
  memcpy(poss.data(), pt.data() + 1, sigma * sizeof(int));
  for (int u = n - 1; --u >= 1; ) if (!cmp[u - 1] && cmp[u]) {
    ids[u] = ++nn;
    nxt[u] = last;
    last = u;
    us[--poss[as[u] - minA]] = u;
  }
  // follow > backwards, from the head of each bucket
  memcpy(poss.data(), pt.data(), sigma * sizeof(int));
  us[poss[as[n - 1] - minA]++] = n - 1;
  for (int i = 0; i < n; ++i) {
    const int u = us[i];
    if (u && !cmp[u - 1]) us[poss[as[u - 1] - minA]++] = u - 1;
  }
  // follow < backwards, from the tail of each bucket
  memcpy(poss.data(), pt.data() + 1, sigma * sizeof(int));
  for (int i = n; --i >= 0; ) {
    const int u = us[i];
    if (u && cmp[u - 1]) us[--poss[as[u - 1] - minA]] = u - 1;
  }
  if (nn) {
    int vsLen = 0;
    vector<int> vs(nn);
    for (const int u : us) if (ids[u]) vs[vsLen++] = u;
    int b = 0;
    vector<int> bs(nn, 0);
    for (int j = 1; j < nn; ++j) {
      // as[v1, w1] (< or =) as[v0, w0]
      int v1 = vs[j - 1], v0 = vs[j];
      const int w1 = nxt[v1], w0 = nxt[v0];
      if (w1 - v1 != w0 - v0) {
        ++b;
      } else {
        for (; ; ++v1, ++v0) {
          if (v1 == n) { ++b; break; }
          if (as[v1] != as[v0]) { ++b; break; }
          if (v1 == w1) break;
        }
      }
      bs[nn - ids[vs[j]]] = b;
    }
    for (int u = 0; u < n; ++u) if (ids[u]) vs[nn - ids[u]] = u;
    const auto sub = suffixArrayRec(bs);
    // put ><, from the tail of each bucket
    memset(us.data(), 0, n * sizeof(int));
    memcpy(poss.data(), pt.data() + 1, sigma * sizeof(int));
    for (int j = nn; --j >= 0; ) {
      const int u = vs[sub[j]];
      us[--poss[as[u] - minA]] = u;
    }
    // follow > backwards, from the head of each bucket
    memcpy(poss.data(), pt.data(), sigma * sizeof(int));
    us[poss[as[n - 1] - minA]++] = n - 1;
    for (int i = 0; i < n; ++i) {
      const int u = us[i];
      if (u && !cmp[u - 1]) us[poss[as[u - 1] - minA]++] = u - 1;
    }
    // follow < backwards, from the tail of each bucket
    memcpy(poss.data(), pt.data() + 1, sigma * sizeof(int));
    for (int i = n; --i >= 0; ) {
      const int u = us[i];
      if (u && cmp[u - 1]) us[--poss[as[u - 1] - minA]] = u - 1;
    }
  }
  return us;
}

// us[i]: i-th suffix
// su[u]: index of as[u, n)
// hs[i]: longest common prefix of as[us[i - 1], n) and as[us[i], n)
struct SuffixArray {
  int n;
  bool rmq;
  vector<int> us, su, hs, bsr;
  SuffixArray() : n(0), rmq(false) {}
  SuffixArray(const string &as, bool rmq_) : rmq(rmq_) { build(as); }
  SuffixArray(const vector<int> &as, bool rmq_) : rmq(rmq_) { build(as); }
  SuffixArray(const vector<long long> &as, bool rmq_) : rmq(rmq_) { build(as); }
  template <class String> void build(const String &as) {
    n = as.size();
    us = suffixArrayRec(as);
    su.resize(n + 1);
    for (int i = 0; i < n; ++i) su[us[i]] = i;
    su[n] = -1;
    hs.assign(n, 0);
    for (int h = 0, u = 0; u < n; ++u) if (su[u]) {
      for (int v = us[su[u] - 1]; v + h < n && as[v + h] == as[u + h]; ++h) {}
      hs[su[u]] = h;
      if (h) --h;
    }
    if (rmq) {
      const int logN = n ? (31 - __builtin_clz(n)) : 0;
      hs.resize((logN + 1) * n - (1 << logN) + 1);
      for (int e = 0; e < logN; ++e) {
        int *hes = hs.data() + e * n;
        for (int i = 0; i <= n - (1 << (e + 1)); ++i) {
          hes[n + i] = min(hes[i], hes[i + (1 << e)]);
        }
      }
      bsr.resize(n + 1);
      bsr[0] = -1;
      for (int i = 1; i <= n; ++i) bsr[i] = bsr[i >> 1] + 1;
    }
  }
  // Returns longest common prefix of as[u, n) and as[v, n).
  //   0 <= u, v <= n
  //   Assumes rmq.
  inline int lcp(int u, int v) const {
    if (u == v) return n - u;
    int i = su[u], j = su[v];
    if (i > j) swap(i, j);
    const int e = bsr[j - i];
    return min(hs[e * n + i + 1], hs[e * n + j + 1 - (1 << e)]);
  }
};
////////////////////////////////////////////////////////////////////////////////


int N, M;
char T[500'010], S[500'010];

string T0, U;
SuffixArray sa;
int cmp(int k0, int k1) {
  if (k0 == k1) return 0;
  if (k0 > k1) return -cmp(k1, k0);
  if (k0 + M <= k1) {
    {
      const int res = sa.lcp(N + 1 + 0, k0);
      if (res < M) return (S[res] < T0[k0 + res]) ? -1 : +1;
    }
    {
      const int res = sa.lcp(k1, N + 1 + 0);
      if (res < M) return (T0[k1 + res] < S[res]) ? -1 : +1;
    }
  } else {
    {
      const int res = sa.lcp(N + 1 + 0, k0);
      if (res < k1 - k0) return (S[res] < T0[k0 + res]) ? -1 : +1;
    }
    {
      const int res = sa.lcp(N + 1 + (k1 - k0), N + 1 + 0);
      if (res < k0 + M - k1) return (S[(k1 - k0) + res] < S[res]) ? -1 : +1;
    }
    {
      const int res = sa.lcp(k0 + M, N + 1 + (k0 + M - k1));
      if (res < k1 - k0) return (T0[(k0 + M) + res] < S[(k0 + M - k1) + res]) ? -1 : +1;
    }
  }
  return 0;
}

int main() {
  for (int numCases; ~scanf("%d", &numCases); ) { for (int caseId = 1; caseId <= numCases; ++caseId) {
    scanf("%d%d", &N, &M);
    scanf("%s", T);
    scanf("%s", S);
    
    vector<Mint> fss[3], gss[3];
    for (int h = 0; h < 3; ++h) {
      fss[h].assign(M, 0);
      gss[h].assign(N, 0);
    }
    for (int i = 0; i < M; ++i) if (S[i] != '?') {
      const int a = S[i] - 'a';
      fss[0][i] = 1;
      fss[1][i] = a;
      fss[2][i] = a*a;
    }
    for (int i = 0; i < N; ++i) if (T[i] != '?') {
      const int a = T[i] - 'a';
      gss[0][i] = 1;
      gss[1][i] = a;
      gss[2][i] = a*a;
    }
    const auto prod02 = middle(fss[0], gss[2]);
    const auto prod11 = middle(fss[1], gss[1]);
    const auto prod20 = middle(fss[2], gss[0]);
    vector<Mint> hs(N - M + 1, 0);
    for (int i = 0; i <= N - M; ++i) {
      hs[i] += prod02[i];
      hs[i] -= 2 * prod11[i];
      hs[i] += prod20[i];
    }
// cerr<<"hs = "<<hs<<endl;
    
    T0 = T;
    for (int i = 0; i < N; ++i) if (T[i] == '?') {
      T0[i] = 'a';
    }
    U = T0 + '`' + S;
    sa = SuffixArray(U, true);
    
    int km = -1;
    for (int k = 0; k <= N - M; ++k) if (!hs[k]) {
      if (!~km || cmp(km, k) > 0) {
        km = k;
      }
    }
    if (~km) {
      string ans = T0;
      for (int i = 0; i < M; ++i) {
        ans[km + i] = S[i];
      }
      puts(ans.c_str());
    } else {
      puts("-1");
    }
  }
#ifndef LOCAL
  break;
#endif
  }
  return 0;
}