#include<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<numeric>
#include<cmath>
#include<utility>
#include<tuple>
#include<cstdint>
#include<cstdio>
#include<iomanip>
#include<map>
#include<queue>
#include<set>
#include<stack>
#include<deque>
#include<unordered_map>
#include<unordered_set>
#include<bitset>
#include<cctype>
#include<chrono>
#include<random>
#include<cassert>
#include<cstddef>
#include<iterator>
#include<string_view>
#include<type_traits>

#ifdef LOCAL
#  include "debug_print.hpp"
#  define debug(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define debug(...) (static_cast<void>(0))
#endif

using namespace std;
#define rep(i,n) for(int i=0; i<(n); i++)
#define rrep(i,n) for(int i=(n)-1; i>=0; i--)
#define FOR(i,a,b) for(int i=(a); i<(b); i++)
#define RFOR(i,a,b) for(int i=(b-1); i>=(a); i--)
#define ALL(v) v.begin(), v.end()
#define RALL(v) v.rbegin(), v.rend()
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );
#define pb push_back
using ll = long long;
using D = double;
using LD = long double;
using P = pair<int, int>;
template<typename T> using PQ = priority_queue<T,vector<T>>;
template<typename T> using minPQ = priority_queue<T, vector<T>, greater<T>>;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
void yesno(bool flag) {cout << (flag?"Yes":"No") << "\n";}

template<typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
    os << p.first << " " << p.second;
    return os;
}
template<typename T, typename U>
istream &operator>>(istream &is, pair<T, U> &p) {
    is >> p.first >> p.second;
    return is;
}

template<typename T>
ostream &operator<<(ostream &os, const vector<T> &v) {
    int s = (int)v.size();
    for (int i = 0; i < s; i++) os << (i ? " " : "") << v[i];
    return os;
}
template<typename T>
istream &operator>>(istream &is, vector<T> &v) {
    for (auto &x : v) is >> x;
    return is;
}
void in() {}
template<typename T, class... U>
void in(T &t, U &...u) {
    cin >> t;
    in(u...);
}
void out() { cout << "\n"; }
template<typename T, class... U, char sep = ' '>
void out(const T &t, const U &...u) {
    cout << t;
    if (sizeof...(u)) cout << sep;
    out(u...);
}
void outr() {}
template<typename T, class... U, char sep = ' '>
void outr(const T &t, const U &...u) {
    cout << t;
    outr(u...);
}

#include "atcoder/convolution.hpp"
#include "atcoder/string.hpp"

/**
 * @brief Sparse-Table(スパーステーブル)
 * @docs docs/sparse-table.md
 */
template< typename T, typename F >
struct SparseTable {
  F f;
  vector< vector< T > > st;
  vector< int > lookup;

  SparseTable() = default;

  explicit SparseTable(const vector< T > &v, const F &f) : f(f) {
    const int n = (int) v.size();
    const int b = 32 - __builtin_clz(n);
    st.assign(b, vector< T >(n));
    for(int i = 0; i < v.size(); i++) {
      st[0][i] = v[i];
    }
    for(int i = 1; i < b; i++) {
      for(int j = 0; j + (1 << i) <= n; j++) {
        st[i][j] = f(st[i - 1][j], st[i - 1][j + (1 << (i - 1))]);
      }
    }
    lookup.resize(v.size() + 1);
    for(int i = 2; i < lookup.size(); i++) {
      lookup[i] = lookup[i >> 1] + 1;
    }
  }

  inline T fold(int l, int r) const {
    int b = lookup[r - l];
    return f(st[b][l], st[b][r - (1 << b)]);
  }
};

template< typename T, typename F >
SparseTable< T, F > get_sparse_table(const vector< T > &v, const F &f) {
  return SparseTable< T, F >(v, f);
}

void solve(){
    int n,m; string s,t; in(n,m,s,t);
    vector<ll> x3_cs(n+1),x_rev(n),x2_rev(n),y(m),y2(m);
    rep(i,n) {
        int val = (s[i] == '?' ? 0 : (s[i]-'a')+1);
        x3_cs[i+1] = x3_cs[i] + val*val*val;
        x_rev[n-1-i] = val;
        x2_rev[n-1-i] = val*val;

    }
    rep(i,m) {
        int val = (t[i]-'a')+1;
        y[i] = val;
        y2[i] = val*val;
    }

    vector<int> pos_match;
    auto xxy = atcoder::convolution_ll(x2_rev, y);
    auto xyy = atcoder::convolution_ll(x_rev, y2);
    rep(i,n-m+1) {
        ll sum = x3_cs[i+m] - x3_cs[i] - 2 * xxy[n-1-i] + xyy[n-1-i];
        if (sum == 0) pos_match.pb(i);
    }

    if (pos_match.empty()) {
        out("-1");
        return;
    }

    string sr = s;
    rep(i,n) if(sr[i] == '?') sr[i] = 'a';
    auto ztt = atcoder::z_algorithm(t);
    string u = t+sr;
    auto sa = atcoder::suffix_array(u);
    auto lc = atcoder::lcp_array(u, sa);
    vector<int> sa_inv(n+m);
    rep(i,n+m) sa_inv[sa[i]] = i;
    auto spt = get_sparse_table(lc, [](auto a, auto b){return min(a,b);});

    int idx = pos_match[0];
    FOR(i,1,pos_match.size()) {
        int pos = pos_match[i];
        if (idx+m <= pos) break;

        int p = sa_inv[0], q = sa_inv[m+pos];
        if (p > q) swap(p,q);
        int len = spt.fold(p,q);
        chmin(len, n-pos);
        if (len < n-pos) {
            char a = t[len], b = sr[idx+len];
            if (a > b) {
                idx = pos;
            }
            continue;
        }

        len = ztt[pos-idx];
        if (len < n-pos+idx) {
            char a = t[len+pos-idx], b = t[len];
            if (a > b) {
                idx = pos;
            }
            continue;
        }

        p = sa_inv[idx+m+m], q = sa_inv[n-pos];
        if (p > q) swap(p,q);
        len = spt.fold(p,q);
        chmin(len, n-pos);
        if (len < n-pos) {
            char a = sr[len+idx+m], b = t[n-pos+len];
            if (a > b) {
                idx = pos;
            }
            continue;
        }
    }

    string ans = sr;
    rep(i,m) ans[i+idx] = t[i];
    out(ans);
}

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int ntcs; in(ntcs);
    while(ntcs--) {
        solve();
    }
}