#include <iostream>
#include <string>

using namespace std;

int main() {
    int t;
    cin >> t;
    while (t--) {
        int n, m;
        string s1, s2;
        cin >> n >> m >> s1 >> s2;

        bool found = false;
        int pos = -1;
        for (int i = 0; i + m <= n; i++) {
            bool match = true;
            for (int j = 0; j < m; j++) {
                if (s1[i+j] != s2[j] && s1[i+j] != '?') {
                    match = false;
                    break;
                }
            }
            if (match) {
                found = true;
                pos = i;
                break;
            }
        }

        if (!found) {
            cout << "UNRESTORABLE" << endl;
            continue;
        }

        for (int i = 0; i < n; i++) {
            if (i >= pos && i < pos + m) {
                cout << s2[i-pos];
            } else if (s1[i] == '?') {
                cout << 'a';
            } else {
                cout << s1[i];
            }
        }
        cout << endl;
    }
    return 0;
}