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
'''
# Read input from stdin and provide input before running code

name = raw_input('What is your name?\n')
print 'Hi, %s.' % name
'''
#print 'Hello World!'
t=input()
while t>0:
	t-=1
	s1=raw_input()
	s2=raw_input()
	l=""
	for i in range(len(s1)):
		if s1[i]==s2[i]:
			l+="0"
		else:
			l+="1"
			
		
	print l