#include<stdio.h>
#include<string.h>

#define lg 1005

int k, x1, x2, d[lg][lg], a1[100][lg], a2[100][lg], i, j, p1, p2, l1, l2;
char s1[lg], s2[lg];

inline int max(int a, int b){
	if (a > b)
		return a;
	return b;
}
void golire(){
	for (int i = 0; i < x1; i ++)
		for (int j = 0; j < x2; j ++)
			d[i][j] = 0;

	for (int i = 'Z'; i >= 'A'; i --){
		for (int j = 0; j < x1; j ++)
			a1[i][j] = 0;
		for (int j = 0; j < x2; j ++)
			a2[i][j] = 0;
	}
}
int main()
{
	freopen("seif.in", "rt", stdin);
	freopen("seif.out", "wt", stdout);
	
	int teste;

	scanf("%d", &teste);

	while (teste --){
		scanf("%d\n", &k);

		scanf("%s%s", s1, s2);

		x1 = strlen(s1), x2 = strlen(s2);

		for (i = x1-1; i >= 0; i --)
			for (j = x2-1; j >= 0; j --){
				if (s1[i] == s2[j])
					d[i][j] = d[i+1][j+1] + 1;
				else
					d[i][j] = max(d[i+1][j], d[i][j+1]);
				//printf("cel mai mare kkt intre %d si %d este %d\n", i, j, d[i][j]);
			}

		for (j = 'Z'; j >= 'A'; j --){
			for (i = x1-1; i >= 0; i --)
				if (s1[i] == j)
					a1[j][i] = i+1;
				else
					a1[j][i] = a1[j][i+1];
				//printf("aparitia lui %c de la %d este la %d\n", j, i, a1[j][i]);
			for (i = x2-1; i >= 0; i --)
				if (s2[i] == j)
					a2[j][i] = i+1;
				else
					a2[j][i] = a2[j][i+1];
		}
		
		p1 = 0, p2 = 0;
		
		while (p1 < x1 && p2 < x2){
			for (i = 'Z'; i >= 'A'; i --){
				l1 = a1[i][p1];
				l2 = a2[i][p2];
				//printf("sunt la %c cu %d si %d si obtin %d %d  -->", i, p1, p2, l1, l2);

				if (l1 && l2){
					l1 --, l2 --;

					if (d[l1+1][l2+1] >= k-1){
						k --;
						//printf("am intrat---->\n");
						printf("%c", i);
						
						p1 = l1+1, p2 = l2+1;
						break;
					}
				}
				//printf("\n");
			}

			if (i == 64)
				break;
		}
		printf("\n");

		golire();
	}

	return 0;
}