#include <bits/stdc++.h>
using namespace std;

ifstream fi("seif.in");
ofstream fo("seif.out");

const int N = 1024, S = 26;

int dp[N][N], na[N][S], nb[N][S];
char a[N], b[N];

int n, m, k;

void solve() {
	int x, y;
	bool flag;

	fi >> k >> (a + 1) >> (b + 1);

	n = strlen(a + 1);
	m = strlen(b + 1);

	memset(dp, 0x00, sizeof dp);
	memset(na, 0x00, sizeof na);
	memset(nb, 0x00, sizeof nb);

	for (int i = n; i >= 1; --i)
	for (int j = m; j >= 1; --j)
		if (a[i] == b[j])
			dp[i][j] = dp[i + 1][j + 1] + 1;
		else
			dp[i][j] = max(dp[i + 1][j], dp[i][j + 1]);

	for (int i = n; i >= 1; --i) {
		for (int ch = 0; ch < S; ++ch)
			na[i][ch] = na[i + 1][ch];
		na[i][a[i] - 'A'] = i; }

	for (int i = m; i >= 1; --i) {
		for (int ch = 0; ch < S; ++ch)
			nb[i][ch] = nb[i + 1][ch];
		nb[i][b[i] - 'A'] = i; }

	x = y = 1;
	do {
		flag = false;
		for (int ch = 25; ch >= 0; --ch)
			if (na[x][ch] && nb[y][ch] && dp[na[x][ch] + 1][nb[y][ch] + 1] >= k - 1) {
				fo << char(ch + 'A');
				x = na[x][ch] + 1;
				y = nb[y][ch] + 1;
				flag = true;
				--k;
				break; } }
	while (flag);

	fo << '\n'; }
	

int main() {
	int tsk;

	fi >> tsk;
	while (tsk--)
		solve();

	return 0; }