#include <bits/stdc++.h>

using namespace std;

#define rep(i, a, b)	for (int i(a); i <= (b); ++i)

#define dec(i, a, b)	for (int i(a); i >= (b); --i)

const int N = 1e5 + 10;

string s[N];

int T;

int n;

int ans;

int main(){

	std::ios::sync_with_stdio(false);

	cin >> T;

	while (T--){

		cin >> n;

		int id;

		int maxv = 0;

		for(int i = 1; i <= n; i++) {

			cin >> s[i];

			if (s[i].size() > maxv) {

				maxv = s[i].size();

				id = i;

			}

		}

		ans = 1;

		rep(i, 1, n) if (s[id].find(s[i]) == -1){ ans = 0; break;}

		if (ans) cout << s[id] << endl;

		else cout << "No" << endl;

	}

	return 0;

}

#include <bits/stdc++.h>

using namespace std;

#define rep(i, a, b)	for (int i(a); i <= (b); ++i)

#define dec(i, a, b)	for (int i(a); i >= (b); --i)

#define MP		make_pair

#define fi		first

#define se		second

typedef long long LL;

const int N = 1e5 + 10;

struct node{

	int x, l, r;

} a[N];

int T;

int n, ans;

queue <int> q;

int main(){

	scanf("%d", &T);

	while (T--){

		scanf("%d", &n);

		rep(i, 1, n){

			a[i].l = i - 1;

			scanf("%d", &a[i].x);

			a[i].r = i + 1;

		}

		a[0].r = 1;

		a[n + 1].l = n;

		a[0].x = 0;

		a[n + 1].x = 1e8;

		while (!q.empty()) q.pop();

		rep(i, 1, n) q.push(i);

		while (!q.empty()){

			int now = q.front(); q.pop();

			int suc = a[now].r;

			int pre = a[now].l;

			if (a[now].x > a[suc].x){

				q.push(pre);

				a[pre].r = a[suc].r;

				a[a[suc].r].l = pre;

				a[suc].l = pre;

			}

		}

		ans = 0;

		int now = a[0].r;

		while (now <= n){

			++ans;

			now = a[now].r;

		}

		printf("%d\n", ans);

		now = a[0].r;

		while (now <= n){

			printf("%d ", a[now].x);

			now = a[now].r;

		}

		putchar(10);

	}

	return 0;

}

#include <bits/stdc++.h>

using namespace std;

#define rep(i, a, b)	for (int i(a); i <= (b); ++i)

#define dec(i, a, b)	for (int i(a); i >= (b); --i)

#define MP		make_pair

#define fi		first

#define se		second

typedef long long LL;

LL a[1001000], b[1001000];

LL n;

int T;

int main(){

	for (LL i = 1; i <= 1000000; ++i) a[i] = i * i * i;

	rep(i, 1, 999999) b[i] = a[i + 1] - a[i];

	scanf("%d", &T);

	while (T--){

		scanf("%lld", &n);

		bool fl = false;

		rep(i, 1, 999999) if (b[i] == n){

		       fl = true;

	       		 break;

		}

		if (fl) puts("YES"); else puts("NO");

	}		

	return 0;

}