#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include<iostream>
#include<string>
#include<cstdio>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<bitset>
#include<stack>
#include<unordered_map>
#include<unordered_set>
#include<utility>
#include<cassert>
#include<complex>
#include<numeric>
#include<array>
#include<chrono>
using namespace std;

//#define int long long
typedef long long ll;

typedef unsigned long long ul;
typedef unsigned int ui;
//ll mod = 1;
constexpr ll mod = 998244353;
//constexpr ll mod = 1000000007;
const ll INF = mod * mod;
typedef pair<int, int>P;

#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
#define all(v) (v).begin(),(v).end()
typedef pair<ll, ll> LP;

template<typename T>
void chmin(T& a, T b) {
	a = min(a, b);
}
template<typename T>
void chmax(T& a, T b) {
	a = max(a, b);
}
template<typename T>
vector<T> vmerge(vector<T>& a, vector<T>& b) {
	vector<T> res;
	int ida = 0, idb = 0;
	while (ida < a.size() || idb < b.size()) {
		if (idb == b.size()) {
			res.push_back(a[ida]); ida++;
		}
		else if (ida == a.size()) {
			res.push_back(b[idb]); idb++;
		}
		else {
			if (a[ida] < b[idb]) {
				res.push_back(a[ida]); ida++;
			}
			else {
				res.push_back(b[idb]); idb++;
			}
		}
	}
	return res;
}
template<typename T>
void cinarray(vector<T>& v) {
	rep(i, v.size())cin >> v[i];
}
template<typename T>
void coutarray(vector<T>& v) {
	rep(i, v.size()) {
		if (i > 0)cout << " "; cout << v[i];
	}
	cout << "\n";
}
ll mod_pow(ll x, ll n, ll m = mod) {
	if (n < 0) {
		ll res = mod_pow(x, -n, m);
		return mod_pow(res, m - 2, m);
	}
	if (abs(x) >= m)x %= m;
	if (x < 0)x += m;
	//if (x == 0)return 0;
	ll res = 1;
	while (n) {
		if (n & 1)res = res * x % m;
		x = x * x % m; n >>= 1;
	}
	return res;
}
//mod should be <2^31
struct modint {
	int n;
	modint() :n(0) { ; }
	modint(ll m) {
		if (m < 0 || mod <= m) {
			m %= mod; if (m < 0)m += mod;
		}
		n = m;
	}
	operator int() { return n; }
};
bool operator==(modint a, modint b) { return a.n == b.n; }
bool operator<(modint a, modint b) { return a.n < b.n; }
modint operator+=(modint& a, modint b) { a.n += b.n; if (a.n >= mod)a.n -= (int)mod; return a; }
modint operator-=(modint& a, modint b) { a.n -= b.n; if (a.n < 0)a.n += (int)mod; return a; }
modint operator*=(modint& a, modint b) { a.n = ((ll)a.n * b.n) % mod; return a; }
modint operator+(modint a, modint b) { return a += b; }
modint operator-(modint a, modint b) { return a -= b; }
modint operator*(modint a, modint b) { return a *= b; }
modint operator^(modint a, ll n) {
	if (n == 0)return modint(1);
	modint res = (a * a) ^ (n / 2);
	if (n % 2)res = res * a;
	return res;
}

ll inv(ll a, ll p) {
	return (a == 1 ? 1 : (1 - p * inv(p % a, a)) / a + p);
}
modint operator/(modint a, modint b) { return a * modint(inv(b, mod)); }
modint operator/=(modint& a, modint b) { a = a / b; return a; }
const int max_n = 1 << 20;
modint fact[max_n], factinv[max_n];
void init_f() {
	fact[0] = modint(1);
	for (int i = 0; i < max_n - 1; i++) {
		fact[i + 1] = fact[i] * modint(i + 1);
	}
	factinv[max_n - 1] = modint(1) / fact[max_n - 1];
	for (int i = max_n - 2; i >= 0; i--) {
		factinv[i] = factinv[i + 1] * modint(i + 1);
	}
}
modint comb(int a, int b) {
	if (a < 0 || b < 0 || a < b)return 0;
	return fact[a] * factinv[b] * factinv[a - b];
}
modint combP(int a, int b) {
	if (a < 0 || b < 0 || a < b)return 0;
	return fact[a] * factinv[a - b];
}

ll gcd(ll a, ll b) {
	a = abs(a); b = abs(b);
	if (a < b)swap(a, b);
	while (b) {
		ll r = a % b; a = b; b = r;
	}
	return a;
}
using ld = long double;
//typedef long double ld;
typedef pair<ld, ld> LDP;
const ld eps = 1e-10;
const ld pi = acosl(-1.0);
template<typename T>
void addv(vector<T>& v, int loc, T val) {
	if (loc >= v.size())v.resize(loc + 1, 0);
	v[loc] += val;
}
/*const int mn = 2000005;
bool isp[mn];
vector<int> ps;
void init() {
	fill(isp + 2, isp + mn, true);
	for (int i = 2; i < mn; i++) {
		if (!isp[i])continue;
		ps.push_back(i);
		for (int j = 2 * i; j < mn; j += i) {
			isp[j] = false;
		}
	}
}*/

//[,val)
template<typename T>
auto prev_itr(set<T>& st, T val) {
	auto res = st.lower_bound(val);
	if (res == st.begin())return st.end();
	res--; return res;
}

//[val,)
template<typename T>
auto next_itr(set<T>& st, T val) {
	auto res = st.lower_bound(val);
	return res;
}
using mP = pair<modint, modint>;
mP operator+(mP a, mP b) {
	return { a.first + b.first,a.second + b.second };
}
mP operator+=(mP& a, mP b) {
	a = a + b; return a;
}
mP operator-(mP a, mP b) {
	return { a.first - b.first,a.second - b.second };
}
mP operator-=(mP& a, mP b) {
	a = a - b; return a;
}
LP operator+(LP a, LP b) {
	return { a.first + b.first,a.second + b.second };
}
LP operator+=(LP& a, LP b) {
	a = a + b; return a;
}
LP operator-(LP a, LP b) {
	return { a.first - b.first,a.second - b.second };
}
LP operator-=(LP& a, LP b) {
	a = a - b; return a;
}

mt19937 mt(time(0));

const string drul = "DRUL";
string senw = "SENW";
//DRUL,or SENW
int dx[4] = { 1,0,-1,0 };
int dy[4] = { 0,1,0,-1 };

//-----------------------------------------



//https://github.com/atcoder/ac-library

namespace internal {

    std::vector<int> sa_naive(const std::vector<int>& s) {
        int n = int(s.size());
        std::vector<int> sa(n);
        std::iota(sa.begin(), sa.end(), 0);
        std::sort(sa.begin(), sa.end(), [&](int l, int r) {
            if (l == r) return false;
        while (l < n && r < n) {
            if (s[l] != s[r]) return s[l] < s[r];
            l++;
            r++;
        }
        return l == n;
            });
        return sa;
    }

    std::vector<int> sa_doubling(const std::vector<int>& s) {
        int n = int(s.size());
        std::vector<int> sa(n), rnk = s, tmp(n);
        std::iota(sa.begin(), sa.end(), 0);
        for (int k = 1; k < n; k *= 2) {
            auto cmp = [&](int x, int y) {
                if (rnk[x] != rnk[y]) return rnk[x] < rnk[y];
                int rx = x + k < n ? rnk[x + k] : -1;
                int ry = y + k < n ? rnk[y + k] : -1;
                return rx < ry;
            };
            std::sort(sa.begin(), sa.end(), cmp);
            tmp[sa[0]] = 0;
            for (int i = 1; i < n; i++) {
                tmp[sa[i]] = tmp[sa[i - 1]] + (cmp(sa[i - 1], sa[i]) ? 1 : 0);
            }
            std::swap(tmp, rnk);
        }
        return sa;
    }

    // SA-IS, linear-time suffix array construction
    // Reference:
    // G. Nong, S. Zhang, and W. H. Chan,
    // Two Efficient Algorithms for Linear Time Suffix Array Construction
    template <int THRESHOLD_NAIVE = 10, int THRESHOLD_DOUBLING = 40>
    std::vector<int> sa_is(const std::vector<int>& s, int upper) {
        int n = int(s.size());
        if (n == 0) return {};
        if (n == 1) return { 0 };
        if (n == 2) {
            if (s[0] < s[1]) {
                return { 0, 1 };
            }
            else {
                return { 1, 0 };
            }
        }
        if (n < THRESHOLD_NAIVE) {
            return sa_naive(s);
        }
        if (n < THRESHOLD_DOUBLING) {
            return sa_doubling(s);
        }

        std::vector<int> sa(n);
        std::vector<bool> ls(n);
        for (int i = n - 2; i >= 0; i--) {
            ls[i] = (s[i] == s[i + 1]) ? ls[i + 1] : (s[i] < s[i + 1]);
        }
        std::vector<int> sum_l(upper + 1), sum_s(upper + 1);
        for (int i = 0; i < n; i++) {
            if (!ls[i]) {
                sum_s[s[i]]++;
            }
            else {
                sum_l[s[i] + 1]++;
            }
        }
        for (int i = 0; i <= upper; i++) {
            sum_s[i] += sum_l[i];
            if (i < upper) sum_l[i + 1] += sum_s[i];
        }

        auto induce = [&](const std::vector<int>& lms) {
            std::fill(sa.begin(), sa.end(), -1);
            std::vector<int> buf(upper + 1);
            std::copy(sum_s.begin(), sum_s.end(), buf.begin());
            for (auto d : lms) {
                if (d == n) continue;
                sa[buf[s[d]]++] = d;
            }
            std::copy(sum_l.begin(), sum_l.end(), buf.begin());
            sa[buf[s[n - 1]]++] = n - 1;
            for (int i = 0; i < n; i++) {
                int v = sa[i];
                if (v >= 1 && !ls[v - 1]) {
                    sa[buf[s[v - 1]]++] = v - 1;
                }
            }
            std::copy(sum_l.begin(), sum_l.end(), buf.begin());
            for (int i = n - 1; i >= 0; i--) {
                int v = sa[i];
                if (v >= 1 && ls[v - 1]) {
                    sa[--buf[s[v - 1] + 1]] = v - 1;
                }
            }
        };

        std::vector<int> lms_map(n + 1, -1);
        int m = 0;
        for (int i = 1; i < n; i++) {
            if (!ls[i - 1] && ls[i]) {
                lms_map[i] = m++;
            }
        }
        std::vector<int> lms;
        lms.reserve(m);
        for (int i = 1; i < n; i++) {
            if (!ls[i - 1] && ls[i]) {
                lms.push_back(i);
            }
        }

        induce(lms);

        if (m) {
            std::vector<int> sorted_lms;
            sorted_lms.reserve(m);
            for (int v : sa) {
                if (lms_map[v] != -1) sorted_lms.push_back(v);
            }
            std::vector<int> rec_s(m);
            int rec_upper = 0;
            rec_s[lms_map[sorted_lms[0]]] = 0;
            for (int i = 1; i < m; i++) {
                int l = sorted_lms[i - 1], r = sorted_lms[i];
                int end_l = (lms_map[l] + 1 < m) ? lms[lms_map[l] + 1] : n;
                int end_r = (lms_map[r] + 1 < m) ? lms[lms_map[r] + 1] : n;
                bool same = true;
                if (end_l - l != end_r - r) {
                    same = false;
                }
                else {
                    while (l < end_l) {
                        if (s[l] != s[r]) {
                            break;
                        }
                        l++;
                        r++;
                    }
                    if (l == n || s[l] != s[r]) same = false;
                }
                if (!same) rec_upper++;
                rec_s[lms_map[sorted_lms[i]]] = rec_upper;
            }

            auto rec_sa =
                sa_is<THRESHOLD_NAIVE, THRESHOLD_DOUBLING>(rec_s, rec_upper);

            for (int i = 0; i < m; i++) {
                sorted_lms[i] = lms[rec_sa[i]];
            }
            induce(sorted_lms);
        }
        return sa;
    }

}  // namespace internal

std::vector<int> suffix_array(const std::vector<int>& s, int upper) {
    assert(0 <= upper);
    for (int d : s) {
        assert(0 <= d && d <= upper);
    }
    auto sa = internal::sa_is(s, upper);
    return sa;
}

template <class T> std::vector<int> suffix_array(const std::vector<T>& s) {
    int n = int(s.size());
    std::vector<int> idx(n);
    iota(idx.begin(), idx.end(), 0);
    sort(idx.begin(), idx.end(), [&](int l, int r) { return s[l] < s[r]; });
    std::vector<int> s2(n);
    int now = 0;
    for (int i = 0; i < n; i++) {
        if (i && s[idx[i - 1]] != s[idx[i]]) now++;
        s2[idx[i]] = now;
    }
    return internal::sa_is(s2, now);
}

std::vector<int> suffix_array(const std::string& s) {
    int n = int(s.size());
    std::vector<int> s2(n);
    for (int i = 0; i < n; i++) {
        s2[i] = s[i];
    }
    return internal::sa_is(s2, 255);
}

// Reference:
// T. Kasai, G. Lee, H. Arimura, S. Arikawa, and K. Park,
// Linear-Time Longest-Common-Prefix Computation in Suffix Arrays and Its
// Applications
template <class T>
std::vector<int> lcp_array(const std::vector<T>& s,
    const std::vector<int>& sa) {
    int n = int(s.size());
    assert(n >= 1);
    std::vector<int> rnk(n);
    for (int i = 0; i < n; i++) {
        rnk[sa[i]] = i;
    }
    std::vector<int> lcp(n - 1);
    int h = 0;
    for (int i = 0; i < n; i++) {
        if (h > 0) h--;
        if (rnk[i] == 0) continue;
        int j = sa[rnk[i] - 1];
        for (; j + h < n && i + h < n; h++) {
            if (s[j + h] != s[i + h]) break;
        }
        lcp[rnk[i] - 1] = h;
    }
    return lcp;
}

std::vector<int> lcp_array(const std::string& s, const std::vector<int>& sa) {
    int n = int(s.size());
    std::vector<int> s2(n);
    for (int i = 0; i < n; i++) {
        s2[i] = s[i];
    }
    return lcp_array(s2, sa);
}
struct sparse_table {
private:
	int n;
	int tmp;
	vector<int> ori;
	vector<int> transtmp;
	vector<vector<int>> nodel;
public:
	sparse_table(vector<int> _ori) {
		ori = _ori;
		n = ori.size();
		int cop = n;
		tmp = 0;
		while (cop > 0) {
			tmp++; cop >>= 1;
		}
		nodel.resize(tmp);
		rep(i, tmp)nodel[i].resize(n);
		rep(i, n) {
			nodel[0][i] = ori[i];
		}
		rep(j, tmp - 1) {
			rep(i, n) {
				if (i + (1 << j) < n) {
					nodel[j + 1][i] = min(nodel[j][i], nodel[j][i + (1 << j)]);
				}
			}
		}
		transtmp.resize(n + 1);
		int x = 1;
		int cnt = 0;
		rep1(i, n) {
			while (x * 2 <= i) {
				x *= 2; cnt++;
			}
			transtmp[i] = cnt;
		}
	}
	//[l,r)
	int query(int l, int r) {
		if (r - l == 0)return mod;
		int cnt = transtmp[r - l];
		return min(nodel[cnt][l], nodel[cnt][r - (1 << cnt)]);
	}
};


LDP operator*(const LDP& a, const LDP& b) {
	return LDP{ a.first * b.first - a.second * b.second , a.first * b.second + a.second * b.first };
}
LDP operator+(const LDP& a, const LDP& b) {
	return LDP{ a.first + b.first,a.second + b.second };
}
LDP operator-(const LDP& a, const LDP& b) {
	return LDP{ a.first - b.first,a.second - b.second };
}
//非再帰
//eps=0.01を忘れずに
typedef vector<LDP> poly;
poly dft(poly f, bool inverse = false) {
	int n = f.size(); int i, j, k;
	//bit左右反転
	for (i = 0, j = 1; j < n - 1; j++) {
		for (k = n >> 1; k > (i ^= k); k >>= 1);
		if (i > j)swap(f[i], f[j]);
	}
	for (int m = 2; m <= n; m *= 2) {
		LDP zeta = { cos(2 * pi / (ld)m), sin(2 * pi / (ld)m) };
		if (inverse) {
			zeta = { cos(2 * pi * (m - 1) / (ld)m), sin(2 * pi * (m - 1) / (ld)m) };
		}
		for (i = 0; i < n; i += m) {
			LDP powzeta = { 1,0 };
			for (k = i; k < i + m / 2; k++) {
				LDP t1 = f[k], t2 = powzeta * f[k + m / 2];
				f[k] = t1 + t2; f[k + m / 2] = t1 - t2;
				powzeta = powzeta * zeta;
			}
		}
	}
	if (inverse) {
		for (i = 0; i < n; i++) {
			f[i].first /= (ld)n;
			f[i].second /= (ld)n;
		}
	}
	return f;
}
poly multiply(poly g, poly h) {
	int n = 1; int sz = g.size() + h.size();
	while (n <= sz)n *= 2;
	while (g.size() < n) {
		g.push_back({ 0,0 });
	}
	while (h.size() < n) {
		h.push_back({ 0,0 });
	}
	poly gg = dft(g);
	poly hh = dft(h);
	poly ff;
	rep(i, n) {
		ff.push_back(gg[i] * hh[i]);
	}
	return dft(ff, true);
}
void solve() {
	int n, m; cin >> n >> m;
	string s, t; cin >> s >> t;
	poly fs(n);
	rep(i, n) {
		if (s[i] == '?')fs[i] = { 0,0 };
		else {
			int c = s[i] - 'a';
			ld t = (c + 1) * 2 * pi /(ld) 54;
			fs[i] = { cos(t),sin(t) };
		}
	}
	string rt = t;
	reverse(all(rt));
	poly ft(m);
	rep(i, m) {
		int c = rt[i] - 'a';
		ld t = -(c + 1) * 2 * pi / (ld) 54;
		ft[i] = { cos(t),sin(t) };
	}
	poly f = multiply(fs, ft);
	vector<int> ids;
	vector<int> cnt(n + 1);
	rep(i, n) {
		cnt[i + 1] = cnt[i];
		if (s[i] != '?')cnt[i + 1]++;
	}
	rep(i, n - m + 1) {
		ld val = 0;
		if (i+m-1 < f.size())val = f[i+m-1].first;
		int c = cnt[i + m] - cnt[i];
		//cout << f[i].first<<" "<<f[i].second << " " << c << "\n";
		if (abs(val - c) < eps) {
			ids.push_back(i);
		}
	}
	if (ids.empty()) {
		cout << -1 << "\n"; return;
	}
	string ns = s;
	rep(i, ns.size())if (ns[i] == '?')ns[i] = 'a';
	string al = ns + t;
	vector<int> sa = suffix_array(al);
	vector<int> rev(al.size());
	rep(i, sa.size())rev[sa[i]] = i;
	vector<int> lcp = lcp_array(al, sa);
	sparse_table st(lcp);
	auto query = [&](int i, int j) {
		i = rev[i];
		j = rev[j];
		if (i > j)swap(i, j);
		return st.query(i, j);
	};
	int adt = s.size();
	auto comp = [&](int i, int j) {
		if (i > j)swap(i, j);
		if (j - i >= m) {
			int cc = query(adt, i);
			if (cc < m) {
				assert(t[cc] != ns[i + cc]);
				if (t[cc] < ns[i + cc])return i;
				else return j;
			}
			cc = query(j, adt);
			if (cc < m) {
				assert(t[cc] != ns[j + cc]);
				if (t[cc] < ns[j + cc])return j;
				else return i;
			}
			//same
			return i;
		}
		else {
			int dif = j - i;
			int cc = query(adt, i);
			if (cc < dif) {
				assert(t[cc] != ns[i + cc]);
				if (t[cc] < ns[i + cc])return i;
				else return j;
			}
			cc = query(adt + dif, adt);
			if (cc < m - dif) {
				assert(t[cc] != t[cc + dif]);
				if (t[cc] < t[cc + dif])return j;
				else return i;
			}
			dif = m - dif;
			cc = query(i + m, adt + dif);
			if (cc < m - dif) {
				assert(t[cc + dif] != ns[i + m + cc]);
				if (t[cc + dif] < ns[i + m + cc])return j;
				else return i;
			}
			//same
			return i;
		}
	};
	int ci = ids[0];
	for (int i = 1; i < ids.size(); i++) {
		ci = comp(ci, ids[i]);
	}
	string ans = s;
	rep(j, m) {
		ans[ci + j] = t[j];
	}
	rep(i, n)if (ans[i] == '?')ans[i] = 'a';
	cout << ans << "\n";
}


signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	//cout << fixed << setprecision(10);
	//init_f();
	//init();
	//while(true)
	//expr();
	int t; cin >> t; rep(i, t)
	solve();
	return 0;
}