You are given two very large numbers made up of 1 or 0 only. You have to find the digit by digit XOR of the two numbers, i.e., the i-th digit of the answer is 1 if and only if the i-th digit of the two given numbers differ otherwise the i-th digit of the answer is 0. The number of digits in both the numbers is same.

Input:

First line contains the number of test cases T.

Each test case is represented by two lines representing the two numbers. It is guaranteed that the numbers are made from 0 and 1 only and that their length is same.

Output:

For each test case print the corresponding answer.

Constraints:

1 ≤ T ≤ 100

1 ≤ Number of digits in a number ≤ 10^4

SAMPLE INPUT
2
01110
01100
010
111

SAMPLE OUTPUT
00010
101
# your code goes here
"""author : rjohari23"""

import sys

t = int(sys.stdin.readline())
while t:
	a = raw_input()
	b = raw_input()
	ans = []
	
	for i in range(len(a)):
		res = int(a[i])^int(b[i])
		ans.append(str(res))
	
	print ''.join(ans)
	t = t-1