#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); i++)
#define per(i, n) for (int i = (n)-1; i >= 0; i--)
#define rep2(i, l, r) for (int i = (l); i < (r); i++)
#define per2(i, l, r) for (int i = (r)-1; i >= (l); i--)
#define each(e, v) for (auto &e : v)
#define MM << " " <<
#define pb push_back
#define eb emplace_back
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
#define sz(x) (int)x.size()
using ll = long long;
using pii = pair<int, int>;
using pil = pair<int, ll>;
using pli = pair<ll, int>;
using pll = pair<ll, ll>;

template <typename T>
using minheap = priority_queue<T, vector<T>, greater<T>>;

template <typename T>
using maxheap = priority_queue<T>;

template <typename T>
bool chmax(T &x, const T &y) {
    return (x < y) ? (x = y, true) : false;
}

template <typename T>
bool chmin(T &x, const T &y) {
    return (x > y) ? (x = y, true) : false;
}

template <typename T>
int flg(T x, int i) {
    return (x >> i) & 1;
}

template <typename T>
void print(const vector<T> &v, T x = 0) {
    int n = v.size();
    for (int i = 0; i < n; i++) cout << v[i] + x << (i == n - 1 ? '\n' : ' ');
    if (v.empty()) cout << '\n';
}

template <typename T>
void printn(const vector<T> &v, T x = 0) {
    int n = v.size();
    for (int i = 0; i < n; i++) cout << v[i] + x << '\n';
}

template <typename T>
int lb(const vector<T> &v, T x) {
    return lower_bound(begin(v), end(v), x) - begin(v);
}

template <typename T>
int ub(const vector<T> &v, T x) {
    return upper_bound(begin(v), end(v), x) - begin(v);
}

template <typename T>
void rearrange(vector<T> &v) {
    sort(begin(v), end(v));
    v.erase(unique(begin(v), end(v)), end(v));
}

template <typename T>
vector<int> id_sort(const vector<T> &v, bool greater = false) {
    int n = v.size();
    vector<int> ret(n);
    iota(begin(ret), end(ret), 0);
    sort(begin(ret), end(ret), [&](int i, int j) { return greater ? v[i] > v[j] : v[i] < v[j]; });
    return ret;
}

template <typename S, typename T>
pair<S, T> operator+(const pair<S, T> &p, const pair<S, T> &q) {
    return make_pair(p.first + q.first, p.second + q.second);
}

template <typename S, typename T>
pair<S, T> operator-(const pair<S, T> &p, const pair<S, T> &q) {
    return make_pair(p.first - q.first, p.second - q.second);
}

template <typename S, typename T>
istream &operator>>(istream &is, pair<S, T> &p) {
    S a;
    T b;
    is >> a >> b;
    p = make_pair(a, b);
    return is;
}

template <typename S, typename T>
ostream &operator<<(ostream &os, const pair<S, T> &p) {
    return os << p.first << ' ' << p.second;
}

struct io_setup {
    io_setup() {
        ios_base::sync_with_stdio(false);
        cin.tie(NULL);
        cout << fixed << setprecision(15);
    }
} io_setup;

const int inf = (1 << 30) - 1;
const ll INF = (1LL << 60) - 1;
// const int MOD = 1000000007;
const int MOD = 998244353;

template <typename T>
struct Fast_Fourier_Transform {
    using comp = complex<double>;
    static double pi;
    static vector<comp> r, ir;

    Fast_Fourier_Transform() {}

    static void init() {
        if (!r.empty()) return;
        r.resize(30), ir.resize(30);
        for (int i = 0; i < 30; i++) {
            r[i] = -polar(1.0, pi / (1 << (i + 1)));   // r[i] := 1 の 2^(i+2) 乗根
            ir[i] = -polar(1.0, -pi / (1 << (i + 1))); // ir[i] := 1/r[i]
        }
    }

    static vector<comp> to_comp(vector<T> a) {
        vector<comp> ret(a.size());
        for (int i = 0; i < (int)a.size(); i++) ret[i] = comp(a[i], 0.0);
        return ret;
    }

    static vector<T> to_T(vector<comp> a) {
        vector<T> ret(a.size(), 0);
        for (int i = 0; i < (int)a.size(); i++) ret[i] = a[i].real() + 0.1; // 整数の場合、誤差をケア
        // for(int i = 0; i < (int)a.size(); i++) ret[i] = a[i].real(); // 小数の場合
        return ret;
    }

    static void fft(vector<comp> &a) {
        init();
        int n = a.size();
        assert((n & (n - 1)) == 0);
        for (int k = n; k >>= 1;) {
            comp w = 1;
            for (int s = 0, t = 0; s < n; s += 2 * k) {
                for (int i = s, j = s + k; i < s + k; i++, j++) {
                    comp x = a[i], y = w * a[j];
                    a[i] = x + y, a[j] = x - y;
                }
                w *= r[__builtin_ctz(++t)];
            }
        }
    }

    static void ifft(vector<comp> &a) {
        init();
        int n = a.size();
        assert((n & (n - 1)) == 0);
        a.resize(n);
        for (int k = 1; k < n; k <<= 1) {
            comp w = 1;
            for (int s = 0, t = 0; s < n; s += 2 * k) {
                for (int i = s, j = s + k; i < s + k; i++, j++) {
                    comp x = a[i], y = a[j];
                    a[i] = x + y, a[j] = w * (x - y);
                }
                w *= ir[__builtin_ctz(++t)];
            }
        }
        for (auto &e : a) e /= n;
    }

    static vector<T> convolve(vector<T> a, vector<T> b) {
        int k = (int)a.size() + (int)b.size() - 1, n = 1;
        while (n < k) n <<= 1;
        vector<comp> A = to_comp(a), B = to_comp(b);
        A.resize(n), B.resize(n);
        fft(A), fft(B);
        for (int i = 0; i < n; i++) A[i] *= B[i];
        ifft(A);
        vector<T> c = to_T(A);
        c.resize(k);
        return c;
    }
};

template <typename T>
double Fast_Fourier_Transform<T>::pi = acos(-1.0);

template <typename T>
vector<complex<double>> Fast_Fourier_Transform<T>::r = vector<complex<double>>();

template <typename T>
vector<complex<double>> Fast_Fourier_Transform<T>::ir = vector<complex<double>>();

using FFT = Fast_Fourier_Transform<long long>;

const int D = 500000;
using bs = bitset<500000>;

void solve() {
    int N, M;
    string S, T;
    cin >> N >> M >> S >> T;

    bs a;
    rep(i, 500000) a.set(i);

    rep(t, 26) {
        bs b;
        rep(i, N) {
            if (S[i] == char('a' + t) || S[i] == '?') b.set(i);
        }
        rep(i, M) {
            if (T[i] == char('a' + t)) a &= (b >> i);
        }
    }

    rep(i, N) {
        if (S[i] == '?') S[i] = 'a';
    }

    per(i, N) {
        if (a[i]) {
            rep(j, M) {
                S[i + j] = T[j]; //
            }
            cout << S << '\n';
            return;
        }
    }

    cout << "-1\n";
}

int main() {
    int T;
    cin >> T;

    while (T--) solve();
}