#include <bits/stdc++.h>

using namespace std;

const int N = 1009, SIG = 27;

int dp[N][N];
vector < int > poza[SIG], pozb[SIG];

int main()
{
    ifstream fin("seif.in");
    ofstream fout("seif.out");
    ios_base::sync_with_stdio(NULL);
    fin.tie(0);
    fout.tie(0);
    int t, k;
    fin >> t;
    while (t--) {
        string a, b;
        fin >> k >> a >> b;
        int n = a.size();
        int m = b.size();
        for (int i = n - 1; i >= 0; --i) {
            for (int j = m - 1; j >= 0; --j) {
                if (a[i] == b[j])
                    dp[i][j] = 1 + dp[i + 1][j + 1];
                else
                    dp[i][j] = max(dp[i + 1][j], dp[i][j + 1]);
            }
        }
        string ans("");
        for (int i = 0; i < SIG; ++i)
            poza[i].clear();
        for (int i = 0; i < n; ++i)
            poza[a[i] - 'A'].push_back(i);
        for (int i = 0; i < SIG; ++i)
            pozb[i].clear();
        for (int i = 0; i < m; ++i)
            pozb[b[i] - 'A'].push_back(i);
        int pa(-1), pb(-1);
        bool ok(1);
        while (ok) {
            ok = 0;
            for (int i = SIG - 1; i >= 0; --i) {
                int pas = 1<<9, ra(-1);
                while (pas) {
                    if (ra + pas < poza[i].size() && pa >= poza[i][ra + pas])
                        ra += pas;
                    pas >>= 1;
                }
                if (ra + 1 >= poza[i].size() || poza[i][ra + 1] <= pa)
                    continue;
                pas = 1<<9;
                int rb(-1);
                while (pas) {
                    if (rb + pas < pozb[i].size() && pb >= pozb[i][rb + pas])
                        rb += pas;
                    pas >>= 1;
                }
                if (rb + 1 >= pozb[i].size() || pozb[i][rb + 1] <= pb)
                    continue;
                if (dp[poza[i][ra + 1]][pozb[i][rb + 1]] + ans.size() < k)
                    continue;
                pa = poza[i][ra + 1];
                pb = pozb[i][rb + 1];
                ans.push_back('A' + i);
                ok = 1;
                break;
            }
        }
        assert(ans.size() >= k);
        fout << ans << '\n';
    }
    return 0;
}