#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")

#line 1 "template/template.hpp"

#include<bits/stdc++.h>

using namespace std;

using int64 = long long;

const int mod = 998244353;

const int64 infll = (1LL << 62) - 1;

const int inf = (1 << 30) - 1;

struct IoSetup {
  IoSetup() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);
    cerr << fixed << setprecision(10);
  }
} iosetup;

template< typename T1, typename T2 >
ostream &operator<<(ostream &os, const pair< T1, T2 > &p) {
  os << p.first << " " << p.second;
  return os;
}

template< typename T1, typename T2 >
istream &operator>>(istream &is, pair< T1, T2 > &p) {
  is >> p.first >> p.second;
  return is;
}

template< typename T >
ostream &operator<<(ostream &os, const vector< T > &v) {
  for (int i = 0; i < (int) v.size(); i++) {
    os << v[i] << (i + 1 != v.size() ? " " : "");
  }
  return os;
}

template< typename T >
istream &operator>>(istream &is, vector< T > &v) {
  for (T &in: v) is >> in;
  return is;
}

template< typename T1, typename T2 >
inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }

template< typename T1, typename T2 >
inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }

template< typename T = int64 >
vector< T > make_v(size_t a) {
  return vector< T >(a);
}

template< typename T, typename... Ts >
auto make_v(size_t a, Ts... ts) {
  return vector< decltype(make_v< T >(ts...)) >(a, make_v< T >(ts...));
}

template< typename T, typename V >
typename enable_if< is_class< T >::value == 0 >::type fill_v(T &t, const V &v) {
  t = v;
}

template< typename T, typename V >
typename enable_if< is_class< T >::value != 0 >::type fill_v(T &t, const V &v) {
  for (auto &e: t) fill_v(e, v);
}

template< typename F >
struct FixPoint: F {
  explicit FixPoint(F &&f): F(forward< F >(f)) {}

  template< typename... Args >
  decltype(auto) operator()(Args &&... args) const {
    return F::operator()(*this, forward< Args >(args)...);
  }
};

template< typename F >
inline decltype(auto) MFP(F &&f) {
  return FixPoint< F >{forward< F >(f)};
}

template< typename Mint >
struct NumberTheoreticTransformFriendlyModInt {

  static vector< Mint > roots, iroots, rate3, irate3;

  static int max_base;

  NumberTheoreticTransformFriendlyModInt() = default;

  static void init() {
    if (roots.empty()) {
      const unsigned mod = Mint::get_mod();
      assert(mod >= 3 && mod % 2 == 1);
      auto tmp = mod - 1;
      max_base = 0;
      while (tmp % 2 == 0) tmp >>= 1, max_base++;
      Mint root = 2;
      while (root.pow((mod - 1) >> 1) == 1) {
        root += 1;
      }
      assert(root.pow(mod - 1) == 1);

      roots.resize(max_base + 1);
      iroots.resize(max_base + 1);
      rate3.resize(max_base + 1);
      irate3.resize(max_base + 1);

      roots[max_base] = root.pow((mod - 1) >> max_base);
      iroots[max_base] = Mint(1) / roots[max_base];
      for (int i = max_base - 1; i >= 0; i--) {
        roots[i] = roots[i + 1] * roots[i + 1];
        iroots[i] = iroots[i + 1] * iroots[i + 1];
      }
      {
        Mint prod = 1, iprod = 1;
        for (int i = 0; i <= max_base - 3; i++) {
          rate3[i] = roots[i + 3] * prod;
          irate3[i] = iroots[i + 3] * iprod;
          prod *= iroots[i + 3];
          iprod *= roots[i + 3];
        }
      }
    }
  }

  static void ntt(vector< Mint > &a) {
    init();
    const int n = (int) a.size();
    assert((n & (n - 1)) == 0);
    int h = __builtin_ctz(n);
    assert(h <= max_base);
    int len = 0;
    Mint imag = roots[2];
    if (h & 1) {
      int p = 1 << (h - 1);
      Mint rot = 1;
      for (int i = 0; i < p; i++) {
        auto r = a[i + p];
        a[i + p] = a[i] - r;
        a[i] += r;
      }
      len++;
    }
    for (; len + 1 < h; len += 2) {
      int p = 1 << (h - len - 2);
      { // s = 0
        for (int i = 0; i < p; i++) {
          auto a0 = a[i];
          auto a1 = a[i + p];
          auto a2 = a[i + 2 * p];
          auto a3 = a[i + 3 * p];
          auto a1na3imag = (a1 - a3) * imag;
          auto a0a2 = a0 + a2;
          auto a1a3 = a1 + a3;
          auto a0na2 = a0 - a2;
          a[i] = a0a2 + a1a3;
          a[i + 1 * p] = a0a2 - a1a3;
          a[i + 2 * p] = a0na2 + a1na3imag;
          a[i + 3 * p] = a0na2 - a1na3imag;
        }
      }
      Mint rot = rate3[0];
      for (int s = 1; s < (1 << len); s++) {
        int offset = s << (h - len);
        Mint rot2 = rot * rot;
        Mint rot3 = rot2 * rot;
        for (int i = 0; i < p; i++) {
          auto a0 = a[i + offset];
          auto a1 = a[i + offset + p] * rot;
          auto a2 = a[i + offset + 2 * p] * rot2;
          auto a3 = a[i + offset + 3 * p] * rot3;
          auto a1na3imag = (a1 - a3) * imag;
          auto a0a2 = a0 + a2;
          auto a1a3 = a1 + a3;
          auto a0na2 = a0 - a2;
          a[i + offset] = a0a2 + a1a3;
          a[i + offset + 1 * p] = a0a2 - a1a3;
          a[i + offset + 2 * p] = a0na2 + a1na3imag;
          a[i + offset + 3 * p] = a0na2 - a1na3imag;
        }
        rot *= rate3[__builtin_ctz(~s)];
      }
    }
  }

  static void intt(vector< Mint > &a, bool f = true) {
    init();
    const int n = (int) a.size();
    assert((n & (n - 1)) == 0);
    int h = __builtin_ctz(n);
    assert(h <= max_base);
    int len = h;
    Mint iimag = iroots[2];
    for (; len > 1; len -= 2) {
      int p = 1 << (h - len);
      { // s = 0
        for (int i = 0; i < p; i++) {
          auto a0 = a[i];
          auto a1 = a[i + 1 * p];
          auto a2 = a[i + 2 * p];
          auto a3 = a[i + 3 * p];
          auto a2na3iimag = (a2 - a3) * iimag;
          auto a0na1 = a0 - a1;
          auto a0a1 = a0 + a1;
          auto a2a3 = a2 + a3;
          a[i] = a0a1 + a2a3;
          a[i + 1 * p] = (a0na1 + a2na3iimag);
          a[i + 2 * p] = (a0a1 - a2a3);
          a[i + 3 * p] = (a0na1 - a2na3iimag);
        }
      }
      Mint irot = irate3[0];
      for (int s = 1; s < (1 << (len - 2)); s++) {
        int offset = s << (h - len + 2);
        Mint irot2 = irot * irot;
        Mint irot3 = irot2 * irot;
        for (int i = 0; i < p; i++) {
          auto a0 = a[i + offset];
          auto a1 = a[i + offset + 1 * p];
          auto a2 = a[i + offset + 2 * p];
          auto a3 = a[i + offset + 3 * p];
          auto a2na3iimag = (a2 - a3) * iimag;
          auto a0na1 = a0 - a1;
          auto a0a1 = a0 + a1;
          auto a2a3 = a2 + a3;
          a[i + offset] = a0a1 + a2a3;
          a[i + offset + 1 * p] = (a0na1 + a2na3iimag) * irot;
          a[i + offset + 2 * p] = (a0a1 - a2a3) * irot2;
          a[i + offset + 3 * p] = (a0na1 - a2na3iimag) * irot3;
        }
        irot *= irate3[__builtin_ctz(~s)];
      }
    }
    if (len >= 1) {
      int p = 1 << (h - 1);
      for (int i = 0; i < p; i++) {
        auto ajp = a[i] - a[i + p];
        a[i] += a[i + p];
        a[i + p] = ajp;
      }
    }
    if (f) {
      Mint inv_sz = Mint(1) / n;
      for (int i = 0; i < n; i++) a[i] *= inv_sz;
    }
  }

  static vector< Mint > multiply(vector< Mint > a, vector< Mint > b) {
    int need = a.size() + b.size() - 1;
    int nbase = 1;
    while ((1 << nbase) < need) nbase++;
    int sz = 1 << nbase;
    a.resize(sz, 0);
    b.resize(sz, 0);
    ntt(a);
    ntt(b);
    Mint inv_sz = Mint(1) / sz;
    for (int i = 0; i < sz; i++) a[i] *= b[i] * inv_sz;
    intt(a, false);
    a.resize(need);
    return a;
  }
};

template< typename Mint >
vector< Mint > NumberTheoreticTransformFriendlyModInt< Mint >::roots = vector< Mint >();

template< typename Mint >
vector< Mint > NumberTheoreticTransformFriendlyModInt< Mint >::iroots = vector< Mint >();

template< typename Mint >
vector< Mint > NumberTheoreticTransformFriendlyModInt< Mint >::rate3 = vector< Mint >();

template< typename Mint >
vector< Mint > NumberTheoreticTransformFriendlyModInt< Mint >::irate3 = vector< Mint >();

template< typename Mint >
int NumberTheoreticTransformFriendlyModInt< Mint >::max_base = 0;

template< uint32_t mod, bool fast = false >
struct MontgomeryModInt {
  using mint = MontgomeryModInt;
  using i32 = int32_t;
  using i64 = int64_t;
  using u32 = uint32_t;
  using u64 = uint64_t;

  static constexpr u32 get_r() {
    u32 ret = mod;
    for (i32 i = 0; i < 4; i++) ret *= 2 - mod * ret;
    return ret;
  }

  static constexpr u32 r = get_r();

  static constexpr u32 n2 = -u64(mod) % mod;

  static_assert(r * mod == 1, "invalid, r * mod != 1");
  static_assert(mod < (1 << 30), "invalid, mod >= 2 ^ 30");
  static_assert((mod & 1) == 1, "invalid, mod % 2 == 0");

  u32 x;

  MontgomeryModInt(): x{} {}

  MontgomeryModInt(const i64 &a)
      : x(reduce(u64(fast ? a : (a % mod + mod)) * n2)) {}

  static constexpr u32 reduce(const u64 &b) {
    return u32(b >> 32) + mod - u32((u64(u32(b) * r) * mod) >> 32);
  }

  mint &operator+=(const mint &p) {
    if (i32(x += p.x - 2 * mod) < 0) x += 2 * mod;
    return *this;
  }

  mint &operator-=(const mint &p) {
    if (i32(x -= p.x) < 0) x += 2 * mod;
    return *this;
  }

  mint &operator*=(const mint &p) {
    x = reduce(u64(x) * p.x);
    return *this;
  }

  mint &operator/=(const mint &p) {
    *this *= p.inverse();
    return *this;
  }

  mint operator-() const { return mint() - *this; }

  mint operator+(const mint &p) const { return mint(*this) += p; }

  mint operator-(const mint &p) const { return mint(*this) -= p; }

  mint operator*(const mint &p) const { return mint(*this) *= p; }

  mint operator/(const mint &p) const { return mint(*this) /= p; }

  bool operator==(const mint &p) const { return (x >= mod ? x - mod : x) == (p.x >= mod ? p.x - mod : p.x); }

  bool operator!=(const mint &p) const { return (x >= mod ? x - mod : x) != (p.x >= mod ? p.x - mod : p.x); }

  u32 get() const {
    u32 ret = reduce(x);
    return ret >= mod ? ret - mod : ret;
  }

  mint pow(u64 n) const {
    mint ret(1), mul(*this);
    while (n > 0) {
      if (n & 1) ret *= mul;
      mul *= mul;
      n >>= 1;
    }
    return ret;
  }

  mint inverse() const {
    return pow(mod - 2);
  }

  friend ostream &operator<<(ostream &os, const mint &p) {
    return os << p.get();
  }

  friend istream &operator>>(istream &is, mint &a) {
    i64 t;
    is >> t;
    a = mint(t);
    return is;
  }

  static u32 get_mod() { return mod; }
};

using modint = MontgomeryModInt< mod >;

std::vector< bool > wildcard_pattern_matching(const string &p,
                                              const string &s) {
  using ll = long long;
  using usize = std::size_t;
  using mint = modint;

  const usize n = p.size();
  const usize m = s.size();
  assert(n + m - 1 <= (mod - 1 & ~(mod - 1) + 1));
  assert(std::all_of(p.begin(), p.end(), [](int x) { return -1 <= x < mod; }));
  assert(std::all_of(s.begin(), s.end(), [](int x) { return -1 <= x < mod; }));
  {
    const int max = std::max(*std::max_element(p.begin(), p.end()),
                             *std::max_element(s.begin(), s.end()));
    assert(ll(max) *max < mod);
    assert(ll(max) *max * p.size() < mod);
  }

  std::vector< mint > sum(m - n + 1, mint(0));

  const auto add = [&](const auto f, const auto g) {
    std::vector< mint > x(n), y(m);
    for (usize i = 0; i != n; ++i) {
      x[i] = f(p[n - 1 - i]);
    }
    for (usize i = 0; i != m; ++i) {
      y[i] = g(s[i]);
    }
    const auto z = NumberTheoreticTransformFriendlyModInt< modint >::multiply(x, y);
    for (usize i = 0; i != m - n + 1; ++i) {
      sum[i] += z[n - 1 + i];
    }
  };

  add([](const int v) { return ll(v != -1) * v * v; },
      [](const int v) { return int(v != -1); });
  add([](const int v) { return -2 * int(v != -1) * v; },
      [](const int v) { return int(v != -1) * v; });
  add([](const int v) { return int(v != -1); },
      [](const int v) { return ll(v != -1) * v * v; });

  std::vector< bool > res(m - n + 1);
  for (usize i = 0; i != m - n + 1; ++i) {
    res[i] = sum[i].get() == 0;
  }

  return res;
}

#line 1 "string/rolling-hash.hpp"

/**
 * @brief Rolling-Hash(ローリングハッシュ)
 * @see https://qiita.com/keymoon/items/11fac5627672a6d6a9f6
 * @docs docs/rolling-hash.md
 */
struct RollingHash {
  static const uint64_t mod = (1ull << 61ull) - 1;

  using uint128_t = __uint128_t;

  vector< uint64_t > power;

  const uint64_t base;

  static inline uint64_t add(uint64_t a, uint64_t b) {
    if ((a += b) >= mod) a -= mod;
    return a;
  }

  static inline uint64_t mul(uint64_t a, uint64_t b) {
    uint128_t c = (uint128_t) a * b;
    return add(c >> 61, c & mod);
  }

  static inline uint64_t generate_base() {
    mt19937_64 mt(chrono::steady_clock::now().time_since_epoch().count());
    uniform_int_distribution< uint64_t > rand(1, RollingHash::mod - 1);
    return rand(mt);
  }

  inline void expand(size_t sz) {
    if (power.size() < sz + 1) {
      int pre_sz = (int) power.size();
      power.resize(sz + 1);
      for (int i = pre_sz - 1; i < sz; i++) {
        power[i + 1] = mul(power[i], base);
      }
    }
  }

  explicit RollingHash(uint64_t base = generate_base()): base(base), power{1} {}

  vector< uint64_t > build(const string &s) const {
    int sz = s.size();
    vector< uint64_t > hashed(sz + 1);
    for (int i = 0; i < sz; i++) {
      hashed[i + 1] = add(mul(hashed[i], base), s[i]);
    }
    return hashed;
  }

  template< typename T >
  vector< uint64_t > build(const vector< T > &s) const {
    int sz = s.size();
    vector< uint64_t > hashed(sz + 1);
    for (int i = 0; i < sz; i++) {
      hashed[i + 1] = add(mul(hashed[i], base), s[i]);
    }
    return hashed;
  }

  uint64_t query(const vector< uint64_t > &s, int l, int r) {
    expand(r - l);
    return add(s[r], mod - mul(s[l], power[r - l]));
  }

  uint64_t combine(uint64_t h1, uint64_t h2, size_t h2len) {
    expand(h2len);
    return add(mul(h1, power[h2len]), h2);
  }

  int lcp(const vector< uint64_t > &a, int l1, int r1, const vector< uint64_t > &b, int l2, int r2) {
    int len = min(r1 - l1, r2 - l2);
    int low = 0, high = len + 1;
    while (high - low > 1) {
      int mid = (low + high) / 2;
      if (query(a, l1, l1 + mid) == query(b, l2, l2 + mid)) low = mid;
      else high = mid;
    }
    return low;
  }
};

void beet() {
  int N, M;
  cin >> N >> M;
  string X, Y;
  cin >> X >> Y;
  for (auto &p: X) if (p == '?') p = -1;
  auto Z = wildcard_pattern_matching(Y, X);
  bool f = false;
  for (auto z: Z) f |= z;
  if (!f) {
    cout << -1 << "\n";
    return;
  }
  RollingHash hashed;
  string XA = X;
  for (auto &x: XA) if (x == -1) x = 'a';
  auto xh = hashed.build(XA);
  auto yh = hashed.build(Y);

  int l = -1;
  for (int i = 0; i < (int) Z.size(); i++) {
    if (Z[i]) {
      if (l == -1) {
        l = i;
        continue;
      }
      // [0, p) Y [p + M, )
      auto queryRange = [&](int p, int r) {
        uint64_t lv = hashed.query(xh, 0, min(p, r));
        r -= p;
        if (r <= 0) return lv;
        lv = hashed.combine(lv, hashed.query(yh, 0, min(M, r)), min(M, r));
        r -= M;
        if (r <= 0) return lv;
        lv = hashed.combine(lv, hashed.query(xh, p + M, min(N, p + M + r)), min(N, p + M + r));
        return lv;
      };
      auto queryGet = [&](int p, int r) {
        if (r - p < 0) {
          return XA[r];
        }
        r -= p;
        if (r - M < 0) {
          return Y[r];
        }
        return XA[0];
        
        //r -= M;
        //return XA[p + M + r];
      };
      int low = 0, high = N + 1;
      while (high - low > 1) {
        int mid = (low + high) / 2;
        if (queryRange(i, mid) == queryRange(l, mid)) low = mid;
        else high = mid;
      }
      if (low < N and queryGet(i, low) < queryGet(l, low)) {
        l = i;
      }
    }
  }
  for (int k = 0; k < M; k++) {
    X[k + l] = Y[k];
  }
  for (auto &x: X) if (x == -1) x = 'a';
  cout << X << "\n";
}

int main() {
  int T;
  cin >> T;
  while (T--) {
    beet();
  }
}