#include <iostream>
#include <cstdio>
#include <cstring>
#define MAXN 1050

using namespace std;

int t, k, n, m;
int din[MAXN][MAXN], nxta[MAXN][30], nxtb[MAXN][30];
char a[MAXN]=" ", b[MAXN] = " ";

void prepare(char x[MAXN], int nxt[MAXN][30], int cn)
{
    for (int i = cn; i >= 1; i--) {
        for (int j = 0; j < 26; j++)
            nxt[i][j] = nxt[i+1][j];
        nxt[i][x[i]-'A'] = i;
    }
}

void solve()
{
    memset(din, 0, sizeof din);
    memset(nxta, 0, sizeof nxta);
    memset(nxtb, 0, sizeof nxtb);
    for (int i = n; i >= 1; i--)
        for (int j = m; j >= 1; j--) {
            if (a[i] == b[j])
                din[i][j] = din[i+1][j+1]+1;
            else din[i][j] = -1;
            din[i][j] = max(din[i][j], din[i+1][j]);
            din[i][j] = max(din[i][j], din[i][j+1]);
        }
    prepare(a, nxta, n);
    prepare(b, nxtb, m);
    for (int i = 1, j = 1, let; k >= 0 || i <= n && j <= m; k--) {
        for (let = 25; let >= 0; let--)
            if (nxta[i][let] && nxtb[j][let] && din[nxta[i][let]][nxtb[j][let]] >= k) {
                printf("%c", let+'A');
                i = nxta[i][let]+1;
                j = nxtb[j][let]+1;
                break;
            }
        if (let < 0)
            break;
    }
    printf("\n");
}

int main()
{
    freopen("seif.in", "r", stdin);
    freopen("seif.out", "w", stdout);

    scanf("%d\n", &t);
    while (t--) {
        scanf("%d\n", &k);
        gets(a+1); n = strlen(a+1);
        gets(b+1); m = strlen(b+1);
        solve();
    }

    return 0;
}