#include <fstream>
//#include <iostream>
#include <string>
using namespace std;
const int N = 1005;
const int alphabetSize = 26;
int d[N][N], nextA[alphabetSize][N], nextB[alphabetSize][N];
int n, m, k;
string a;
string b;

ifstream cin("seif.in");
ofstream cout("seif.out");

void solve() {
	for(int i = 1; i <= n; ++i)
	{
		for(int j = 1; j <= m; ++j)
		{
			d[i][j] = 0;
		}
	}
	for(int j = 0; j < alphabetSize; ++j)
	{
		for(int i = 1; i <= n; ++i)
		{
			nextA[j][i] = 0;
		}
	}
	for(int j = 0; j < alphabetSize; ++j)
	{
		for(int i = 1; i <= m; ++i)
		{
			nextB[j][i] = 0;
		}
	}

	for(int i = n; i >= 1; --i)
	{
		for(int j = m; j >= 1; --j)
		{

			d[i][j] = d[i][j + 1];
			
			if(a[i] == b[j] && d[i][j] < d[i + 1][j + 1] + 1)
			{
				d[i][j] = d[i + 1][j + 1] + 1;
			}
			
			if(d[i + 1][j] > d[i][j])
			{
				d[i][j] = d[i + 1][j];
			}
		}
	}
	
	for(int j = 0; j < alphabetSize; ++j)
	{
		for(int i = n; i >= 0; --i)
		{
			if(a[i + 1] - 'A' == j)
			{
				nextA[j][i] = i + 1;
			}
			else
			nextA[j][i] = nextA[j][i + 1];
		}
	}

	for(int j = 0; j < alphabetSize; ++j)
	{
		for(int i = m; i >= 0; --i)
		{
			if(b[i + 1] - 'A' == j)
			{
				nextB[j][i] = i + 1;
			}
			else
			nextB[j][i] = nextB[j][i + 1];
		}
	}

	int i = 0, j = 0;
	while(true) 
	{
		int passed = 0;
		for(int l = alphabetSize; l >= 0; --l)
		{
			if(d[nextA[l][i]][nextB[l][j]] >= k && d[nextA[l][i]][nextB[l][j]]) {
				cout << (char) ('A' + l);
				i = nextA[l][i];
				j = nextB[l][j];
				passed = 1;
				--k;
				break;
			}
		}
		if(!passed) {
			break;
		}
	}
	cout << '\n';
}
int main() {
	int t;
	cin >> t;
	for(;t;--t) {
		cin >> k;
		cin >> a >> b;
		n = a.size();
		m = b.size();
		a.resize(a.size() + 1);
		b.resize(b.size() + 1);
		for(int i = n; i > 0; --i)
		{
			a[i] = a[i - 1];
		}

		for(int i = m; i > 0; --i)
		{
			b[i] = b[i - 1];
		}

		solve();
	}

	return 0;
}