#include <iostream>
#include <cstdio>
#define MAX_INT 1000000007
using namespace std;

int main(void)
{
	int q;
	scanf("%d", &q);
	while (q--)
	{
		int n;
		scanf("%d", &n);
		int a, b, c, d, flag = 0;
		a = b = c = d = MAX_INT;
		while (n--)
		{
			int p, q;
			scanf("%d %d", &p, &q);
			if (p != a && p != b)
			{
				if (a==MAX_INT)
					a = p;
				else if (b==MAX_INT)
					b = p;
				else
				{
					flag = 1;
				}
			}
			if (q != c && q != d)
			{
				if (c==MAX_INT)
					c = q;
				else if (d==MAX_INT)
					d = q;
				else
				{
					flag = 1;
				}
			}
			if (flag == 1)
				break;
		}
		if (flag == 1)
		{
			printf("NO\n");
		}
		else
			printf("YES\n");
	}
	return 0;
}