#include <bits/stdc++.h>
#define FILE_NAME "seif"
#define fast ios_base :: sync_with_stdio(0); cin.tie(0);
#pragma GCC optimize("O3")
#define NMAX 1000010
using namespace std;

ifstream f(FILE_NAME ".in");
ofstream g(FILE_NAME ".out");

typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> pi;
typedef pair<ld,ld> pct;

const ll inf = 1LL << 60;
const ll mod = 1e9 + 7;
const ld eps = 1e-9;


void add(ll &a , ll b)
{
    a += b;
    a %= mod;
}

void sub(ll &a, ll b)
{
    a = (a - b + mod) % mod;
}

int n, m, pd[1100][1100],t,cate,k, nxt[2][1100][30],ok;
string a,b;
char sol[1100];

int main()
{
    f >> t;
    while(t--)
    {
        f >> k;
        f >> a >> b;

        memset(pd, 0, sizeof pd);
        memset(nxt, 0, sizeof nxt);
        a = ' '  + a;
        b = ' '  + b;
        n = a.size() - 1;
        m = b.size() - 1;
        for(int i = n; i >= 1; --i)
            for(int j = m; j >= 1; --j)
                if(a[i] == b[j])
                    pd[i][j] = pd[i+1][j+1] + 1;
                else
                    pd[i][j] = max(pd[i+1][j], pd[i][j+1]);

        for(int i = n; i >= 1; --i)
        {
            for(int c = 0; c <= 25; ++c)
                nxt[0][i][c] = nxt[0][i + 1][c];
            nxt[0][i][ a[i] - 'A' ] = i;
        }

        for(int i = m; i >= 1; --i)
        {
            for(int c = 0; c <= 25; ++c)
                nxt[1][i][c] = nxt[1][i + 1][c];
            nxt[1][i][ b[i] - 'A' ] = i;
        }
        int x = 1,  y = 1;
        do
        {
            ok = 0;
            for(int c = 25; c >= 0; --c)
                if(nxt[0][x][c] && nxt[1][y][c] && pd[nxt[0][x][c] + 1][nxt[1][y][c] +1     ] >= k - 1)
                {
                    g << char(c + 'A');
                    x = nxt[0][x][c] + 1;
                    y = nxt[1][y][c] + 1;
                    ok = 1;
                    k--;
                    break;
                }
        }while(ok);
        g << '\n';
    }
    f.close();
    g.close();
    return 0;
}