#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned long long
#define db double
#define pii pair<int,int>
#define pll pair<ll,ll>
#define ti3 tuple<int,int,int>
#define int128 __int128_t
#define pii128 pair<int128,int128>
const int inf = 1 << 30;
const ll linf = 1e18;
const ll mod = 1e9 + 7;
const db EPS = 1e-10;
const db pi = acos(-1);
template<class T> bool chmin(T& x, T y){
    if(x > y) {
        x = y;
        return true;
    } else return false;
}
template<class T> bool chmax(T& x, T y){
    if(x < y) {
        x = y;
        return true;
    } else return false;
}

// overload macro
#define CAT( A, B ) A ## B
#define SELECT( NAME, NUM ) CAT( NAME, NUM )

#define GET_COUNT( _1, _2, _3, _4, _5, _6 /* ad nauseam */, COUNT, ... ) COUNT
#define VA_SIZE( ... ) GET_COUNT( __VA_ARGS__, 6, 5, 4, 3, 2, 1 )

#define VA_SELECT( NAME, ... ) SELECT( NAME, VA_SIZE(__VA_ARGS__) )(__VA_ARGS__)

// rep(overload)
#define rep( ... ) VA_SELECT(rep, __VA_ARGS__)
#define rep2(i, n) for (decay_t<decltype(n)> i = 0; i < n; i++)
#define rep3(i, a, b) for (decay_t<decltype(a)> i = a; i < b; i++)
#define rep4(i, a, b, c) for (decay_t<decltype(a)> i = a; i < b; i += c)

// rrep(overload)
#define rrep( ... ) VA_SELECT(rrep, __VA_ARGS__)
#define rrep2(i, n) for (decay_t<decltype(n)> i = n - 1; i >= 0; i--)
#define rrep3(i, a, b) for (decay_t<decltype(a)> i = b - 1; i >= a; i--)
#define rrep4(i, a, b, c) for (decay_t<decltype(a)> i = b - 1; i >= a; i -= c)

// for_earh
#define fore(e, v) for (auto&& e : v)

// vector
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()

vector<int> Z_algorithm(string S, string T = "") {
    if (T == "") T = S;
    S += '$';
    S += T;
    vector<int> Z(S.size());
    Z[0] = S.size();
    int i = 1, j = 0;
    while(i < (int)S.size()) {
        while(i + j < (int)S.size() && S[j] == S[i + j]) j++;
        Z[i] = j;
        if (j == 0) {
            i++;
            continue;
        }
        int k = 1;
        while (k < j && k + Z[k] < j) {
            Z[i + k] = Z[k];
            k++;
        }
        i += k;
        j -= k;
    }
    vector<int> res(T.size());
    copy(Z.end() - T.size(), Z.end(), res.begin());
    return res;
}

vector<int> Z_algorithm_ques(string S, string T = "") {
    if (T == "") T = S;
    S += '$';
    S += T;
    vector<int> Z(S.size());
    Z[0] = S.size();
    int i = 1, j = 0;
    while(i < (int)S.size()) {
        while(i + j < (int)S.size() && (S[j] == S[i + j] || S[j] == '?' || S[i + j] == '?')) j++;
        Z[i] = j;
        if (j == 0) {
            i++;
            continue;
        }
        int k = 1;
        while (k < j && k + Z[k] < j) {
            Z[i + k] = Z[k];
            k++;
        }
        i += k;
        j -= k;
    }
    vector<int> res(T.size());
    copy(Z.end() - T.size(), Z.end(), res.begin());
    return res;
}

void solve() {
    int N, M;
    string S, T;
    cin >> N >> M >> S >> T;
    auto v1 = Z_algorithm(T, S);
    auto v2 = Z_algorithm_ques(T, S);
    rep (i, N) {
        if (v1[i] == M) {
            rep (i, N) if (S[i] == '?') S[i] = 'a';
            cout << S << "\n";
            return;
        }
    }

    rrep (i, N) {
        if (v2[i] >= M) {
            string ans = S.substr(0, i);
            ans += T;
            ans += S.substr(i + T.size());
            rep (i, N) if (ans[i] == '?') ans[i] = 'a';
            cout << ans << "\n";
            return;
        }
    }

    cout << -1 << "\n";
}

int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    cout << fixed << setprecision(20);
    int t;
    cin >> t;
    while (t--) solve();
    return 0;
}