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

#define lg 1005

int k, n1, n2, nr, i, j, d[lg][lg], dr[95][lg], st[95][lg], p1, p2, h, l1, l2;
char s1[lg], s2[lg], sir[lg];
inline int max(int a, int b){
	if (a > b)
		return a;
	return b;
}
void gol(){
	for (int i = 0; i <= nr; i ++)
		sir[i] = 0;
	for (int i = 0; i < n1; i ++)
		for (int j = 0; j < n2; j ++)
			d[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", s1);
		scanf("%s", s2);
		
		n1 = strlen(s1), n2 = strlen(s2);
		
		for (i = n1-1; i >= 0; i --)
			for (j = n2-1; 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]);
		
		for (i = 'Z'; i >= 'A'; i --)
			for (j = n1-1; j >= 0; j --)
				if (s1[j] == i)
					dr[i][j] = j+1;
				else
					dr[i][j] = dr[i][j+1];
		for (i = 'Z'; i >= 'A'; i --)
			for (j = n2-1; j >= 0; j --)
				if (s2[j] == i)
					st[i][j] = j+1;
				else
					st[i][j] = st[i][j+1];
		
		l1 = 0, l2 = 0;
		while (l1 < n1-1 && l2 < n2-1)
			for (i = 'Z'; i >= 'A'; i --){
				p1 = dr[i][l1];
				p2 = st[i][l2];
				
				if (p1 && p2){
					p1 --, p2 --;
					
					if (d[p1+1][p2+1] >= k-1){
						k --;
						printf("%c", i);
						
						l1 = p1+1, l2 = p2+1;
						break;
					}
				}
			}
		printf("\n");
		
		gol();
	}
	
	return 0;
}