#include <bits/stdc++.h>
#define nmax 1005
#define inf 1e4

using namespace std;

ifstream fin("seif.in");
ofstream fout("seif.out");

int q;
int n, m, K;
char s1[nmax], s2[nmax];

int dp[nmax][nmax];
int next1[nmax][30], next2[nmax][30];

void prec()
{
    int i,j;
    for(i = 1; i <= n+1; i++)
        for(j = 1; j <= m+1; j++)
            dp[i][j] = 0;
    for(i = n; i >= 1; i--)
        for(j = m; j >= 1; j--)
            if(s1[i] == s2[j])
                dp[i][j] = 1 + dp[i+1][j+1];
            else
                dp[i][j] = max(dp[i+1][j],dp[i][j+1]);
    for(i = 0; i < 26; i++)
        next1[n+1][i] = next2[m+1][i] = nmax - 3;
    for(i = n; i >= 1; i--)
    {
        for(j = 0; j < 26; j++)
            next1[i][j] = next1[i+1][j];
        next1[i][s1[i]-'A'] = i;
    }
    for(i = m; i >= 1; i--)
    {
        for(j = 0; j < 26; j++)
            next2[i][j] = next2[i+1][j];
        next2[i][s2[i]-'A'] = i;
    }
}

void solve()
{
    int p1 = 1, p2 = 1;
    while (p1 <= n && p2 <= m)
    {
        int ch;
        bool gasit = 0;
        for (ch = 25; ch >= 0 && !gasit; ch--)
        {
            int n1 = next1[p1][ch];
            int n2 = next2[p2][ch];
            if (dp[n1][n2] >= K && n1 <= n && n2 <= m)
            {
                gasit = 1;
                K--;
                fout << s1[n1];
                p1 = n1 + 1;
                p2 = n2 + 1;
            }
        }
        if (ch == -1 && !gasit)
            break; //stop
    }
    fout << "\n";
}

int main()
{
    fin >> q;
    while (q--)
    {
        fin >> K;
        fin >> (s1 + 1);
        fin >> (s2 + 1);
        n = strlen(s1 + 1);
        m = strlen(s2 + 1);
        prec();
        solve();
    }
    return 0;
}