#include <cstdio>
#include <cstring>
#include <iostream>

#define DIM 1024

using namespace std;

int T, K, N, M, C[DIM][DIM], nextA[DIM][35], nextB[DIM][35];
char A[DIM], B[DIM];

int main()
{
	FILE *fin = fopen("seif.in", "r");
	FILE *fout = fopen("seif.out", "w");

	fscanf(fin, "%d", &T);
	for (int i = 1; i <= T; i++)
	{
		char ch;
		fscanf(fin, "%d", &K);
		fscanf(fin, "%c%s", &ch, A);
		fscanf(fin, "%c%s", &ch, B);
//		cout << A << " " << B << "\n";
		N = strlen(A);
		M = strlen(B);
		memset(nextA, -1, sizeof(nextA));
		memset(nextB, -1, sizeof(nextB));
		memset(C, 0, sizeof(C));

		for (int i = N - 1; i >= 0; i--)
			for (int j = 0; j < 26; j++)
				if (A[i] == j + 'A')
					nextA[i][j] = i;
				else
					nextA[i][j] = nextA[i + 1][j];
		for (int i = M - 1; i >= 0; i--)
			for (int j = 0; j < 26; j++)
				if (B[i] == j + 'A')
					nextB[i][j] = i;
				else
					nextB[i][j] = nextB[i + 1][j];
		for (int i = N - 1; i >= 0; i--)
			for (int j = M - 1; j >= 0; j--)
				if (A[i] == B[j])
					C[i][j] = C[i + 1][j + 1] + 1;
				else
					C[i][j] = C[i + 1][j] > C[i][j + 1] ? C[i + 1][j] : C[i][j + 1];
		int i = 0, j = 0, ok = 1;
		while (ok)
		{
			ok = 0;
			for (int k = 25; k >= 0 && !ok; k--)
				if (nextA[i][k] != -1 && nextB[j][k] != -1)
				{
					if (C[nextA[i][k]][nextB[j][k]] < K) continue;
					fprintf(fout, "%c", k + 'A');
					i = nextA[i][k] + 1;
					j = nextB[j][k] + 1;
					ok = 1;
				}
			K--;
		}
		fprintf(fout, "\n");
	}

	fclose(fin);
	fclose(fout);
	return 0;
}