#include <iostream>
#include <fstream>
using namespace std;
ifstream in("seif.in");
ofstream out("seif.out");
const int maxn = 1005;
int next1[maxn][maxn];
int next2[maxn][maxn];
int dp[maxn][maxn];
string A, B;

void solve()
{
    for(int i = 0; i < maxn; i++)
    {
        for(int j = 0; j < maxn; j++)
            dp[i][j] = 0;
        for(int lit = 1; lit <= 26; lit++)
        {
            next1[i][lit] = 0;
            next2[i][lit] = 0;
        }
    }
    int k;
    in >> k;
    in >> A >> B;
    int n = A.size();
    int m = B.size();
    A = " " + A;
    B = " " + B;
    for(int i = n; i >= 1; i--)
    {
        for(int j = m; j >= 1; j--)
        {
            if(A[i] != B[j])
                dp[i][j] = max(dp[i + 1][j], dp[i][j + 1]);
            else
                dp[i][j] = dp[i + 1][j + 1] + 1;
        }
    }
    for(int lit = 1; lit <= 26; lit++)
    {
        for(int i = n; i >= 1; i--)
        {
            if(A[i] - 'A' + 1 == lit)
                next1[i][lit] = i;
            else
                next1[i][lit] = next1[i + 1][lit];
        }
        for(int i = m; i >= 1; i--)
        {
            if(B[i] - 'A' + 1 == lit)
                next2[i][lit] = i;
            else
                next2[i][lit] = next2[i + 1][lit];
        }
    }
    int poz1 = 1;
    int poz2 = 1;
    bool gasit = 1;
    while(gasit)
    {
        gasit = 0;
        for(int lit = 26; lit >= 1; lit--)
        {
            if(next1[poz1][lit] != 0 && next2[poz2][lit] != 0 && dp[next1[poz1][lit]][next2[poz2][lit]] >= k)
            {
                k = max(k - 1, 0);
                poz1 = next1[poz1][lit] + 1;
                poz2 = next2[poz2][lit] + 1;
                gasit = 1;
                out << (char)(lit + 'A' - 1);
            }
        }
    }
    out << "\n";
}

int main()
{
    int T;
    in >> T;
    for(int i = 1; i <= T; i++)
        solve();
    return 0;
}