// 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;
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)
        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();
    std::string s[n + 5][n + 5];
    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;
return 0;
    // system("pause");
}