#include <bits/stdc++.h>

using namespace std;



ifstream fin("seif.in");

ofstream fout("seif.out");



const int MAX = 1000;

int dp[MAX + 1][MAX + 1];

int nextA[MAX + 1][26];

int nextB[MAX + 1][26];



int main() {

    int t; fin >> t;

    while (t--) {

        int k; fin >> k;

        string a; fin >> a; int m = a.size();

        string b; fin >> b; int n = b.size();



        memset(dp, 0, sizeof(dp));

        for (int i = m - 1; i >= 0; i--)

            for (int j = n - 1; j >= 0; 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 x = 0; x < 26; x++)

            nextA[m][x] = m;

        for (int i = m - 1; i >= 0; i--) {

            for (int x = 0; x < 26; x++)

                nextA[i][x] = nextA[i + 1][x];

            nextA[i][a[i] - 'A'] = i;

        }

        for (int x = 0; x < 26; x++)

            nextB[n][x] = n;

        for (int j = n - 1; j >= 0; j--) {

            for (int x = 0; x < 26; x++)

                nextB[j][x] = nextB[j + 1][x];

            nextB[j][b[j] - 'A'] = j;

        }



        for (int i = 0, j = 0; k >= 0 || (i <= m && j <= n); k--) {

            bool ok = false;

            for (int x = 25; x >= 0; x--)

                if (nextA[i][x] < m && nextB[j][x] < n && dp[nextA[i][x]][nextB[j][x]] >= k) {

                    i = nextA[i][x] + 1;

                    j = nextB[j][x] + 1;

                    fout << (char) (x + 'A');

                    ok = true;

                    break;

                }

            if (!ok)

                break;

        }

        fout << '\n';

    }



    fout.close();

    return 0;

}