// Coded by hjxddl
    #include <bits/stdc++.h>
    #define ll   long long
    #define db   double
    #define v(x) std::vector<x>
    const int N = 2e5 + 5;
    int ans[60], n;
    int ans1[60][60];
    std::string s[60][60];
    std::map<std::pair<int, int>, v(int)> mp;
    std::map<char, int> id;
    std::map<int, char> rid;
    v(int) cnt1, cnt2, cnt3, cnt4;
    bool dfs(int x) {
        if (x == n + 1) {
            v(int) cnt(n * n + 100);
            int ans2[60];
            for (int i = 0; i < n; i++)
                ans2[ans[i]] = i;
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < n; j++) {
                    cnt[i * j]++;
                    if (s[i][j].size() == 1)
                        cnt[ans2[id[s[i][j][0]]]]--;
                    else
                        cnt[ans2[id[s[i][j][0]]] * n + ans2[id[s[i][j][1]]]]--;
                }
            }
            for (int i = 0; i <= n * n; i++)
                if (cnt[i]) return 0;
            return 1;
        }
        v(int) &num = mp[{cnt3[x], cnt4[x]}];
        for (auto &y : num) {
            // std::cerr << x << " " << y << " " << ans[y] << '\n';
            if (ans[y]) continue;
            ans[y] = x;
            if (dfs(x + 1)) return 1;
            ans[y] = 0;
        }
        return 0;
    }
    void init() {
        for (int i = 0; i < n; i++)
            ans[i] = 0;
        mp.clear();
        cnt1 = cnt2 = cnt3 = cnt4 = v(int)(n + 5);
    }
    void solve() {
        std::cin >> n;
        init();
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                std::cin >> s[i][j];
                cnt1[i * j % n]++;
                if (i * j / n)
                    cnt2[i * j / n]++;
                if (s[i][j].size() == 1) {
                    cnt3[id[s[i][j][0]]]++;
                } else {
                    cnt3[id[s[i][j][1]]]++;
                    cnt4[id[s[i][j][0]]]++;
                }
            }
        }
        for (int i = 0; i < n; i++)
            mp[{cnt1[i], cnt2[i]}].push_back(i);
        // for (auto [_, x] : mp) {
        //     for (auto it : x) {
        //         std::cerr << it << " " << _.first << " " << _.second << '\n';
        //     }
        // }
        // for (int i = 1; i <= n; i++) {
        //     std::cerr << i << " " << cnt3[i] << " " << cnt4[i] << '\n';
        // }
        dfs(1);
        for (int i = 0; i < n; i++) {
            std::cout << rid[ans[i]];
        }
        std::cout << '\n';
    }
    int main() {
        std::ios::sync_with_stdio(0);
        std::cin.tie(0), std::cout.tie(0);
        for (int i = 0; i <= 25; i++) {
            id['a' + i] = i + 1;
            rid[i + 1] = char('a' + i);
        }
        for (int i = 26; i <= 51; i++) {
            id['A' + i - 26] = i + 1;
            rid[i + 1] = char('A' + i - 26);
        }
        int t = 1;
        std::cin >> t;
        while (t--) {
            solve();
        }
        std::cout << std::flush;
        // system("pause");
    }