#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define Mp make_pair
#define pb push_back
#define SZ(a) (int(a.size()))

typedef long long ll;
typedef double db;
typedef std::pair<int, int> pii;
typedef std::vector<int> vi;
#define log(...) fprintf(stderr, __VA_ARGS__)
std::mt19937_64 gen(std::chrono::system_clock::now().time_since_epoch().count());
ll get(ll l, ll r) { std::uniform_int_distribution<ll> dist(l, r); return dist(gen); }

void solve() {
    int n;
    cin >> n;
    vector<string> s(n * n); vi o;
    vector<vi> cnt(2, vi(n)), vcnt(2, vi(n));
    auto id = [&](char ch) {
        if(islower(ch)) return ch - 'a';
        else return ch - 'A' + 26;
    };
    for(int i = 0; i < n; i++)
        for(int j = 0; j < n; j++) {
            int num = i * j, hi = num / n, lo = num % n;
            o.pb(num); cnt[0][lo]++; if(hi) cnt[1][hi]++;
            string t; cin >> t; s[i * n + j] = t;
            if(SZ(t) == 1) vcnt[0][id(t[0])]++;
            else vcnt[0][id(t[1])]++, vcnt[1][id(t[0])]++;
        }
    sort(o.begin(), o.end());
    map<pair<int, int>, vi> mp, vmp;
    for(int i = 0; i < n; i++) {
        mp[Mp(cnt[0][i], cnt[1][i])].pb(i);
        vmp[Mp(vcnt[0][i], vcnt[1][i])].pb(i);
    }
    vector<vi> ve, vve;
    for(auto [p, v] : mp) ve.pb(v);
    for(auto [p, v] : vmp) vve.pb(v);
    vi tran(n); int fl = 0;
    auto eval = [&](string s) {
        int res = 0;
        for(auto ch : s)
            res = res * n + tran[id(ch)];
        return res;
    };
    auto chk = [&]() {
        vi oo;
        for(int i = 0; i < n * n; i++)
            oo.pb(eval(s[i]));
        sort(oo.begin(), oo.end());
        return o == oo;
    };
    auto dfs = [&](auto self, int x) {
        if(x == SZ(ve)) {
            if(chk()) fl = 1;
            return;
        }
        sort(vve[x].begin(), vve[x].end());
        do {
            for(int i = 0; i < SZ(vve[x]); i++) {
                tran[vve[x][i]] = ve[x][i];
            }
            self(self, x + 1);
            if(fl) return;
        } while(next_permutation(vve[x].begin(), vve[x].end()));
    };
    dfs(dfs, 0);
    string ans(n, ' ');
    auto rid = [&](int i) -> char {
        return i < 26 ? i + 'a' : i - 26 + 'A';
    };
    for(int i = 0; i < n; i++) {
        ans[tran[i]] = rid(i);
    }
    cout << ans << '\n';
}
signed main() {
    atexit([](){cerr << "time: " << (db)clock()/CLOCKS_PER_SEC << "s\n";});
    ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
    int _; cin >> _; for(int cas = 1; cas <= _; cas++) solve();
    return 0;
}