> #include "stdio.h"
> #include "string.h"
> #define N 61
> 
> int main()
> {
> 	int m, nCases, i, j, k, flg;
> 	char maxL, base[10][N], suq[N], fsuq[N];
> 	scanf("%d", &nCases);
> 	while (nCases--) {
> 		scanf("%d", &m);
> 		for (i = 0; i < m; i++)
> 			scanf("%s", base[i]);
> 		maxL = 0;
> 		for (i = 0; i < N - 3; i++) {
> 			for (j = 3; j < N - i; j++) {
> 				strncpy(suq, base[0] + i, j);
> 				suq[j] = '\0';
> 				flg = 1;
> 				for (k = 1; k < m; k++) {
> 					if (strstr(base[k], suq) == NULL) {
> 						flg = 0;
> 						break;
> 					}
> 				}
> 				if (flg && j > maxL) {
> 					maxL = j;
> 					strcpy(fsuq, suq);
> 				}
> 				else if (flg && j == maxL) 
> 					if (strcmp(suq, fsuq) < 0)
> 						strcpy(fsuq, suq);
> 			}
> 		}
> 		if (maxL == 0) printf("no significant commonalities\n");
> 		else printf("%s\n", fsuq);
> 	}
> 	return 0;
> }