nclude<bits/stdc++.h>
using namespace std;
int main() {
int t;
cin>>t;
while(t--){
string n1,n2;
//long long p=1;
cin>>n1>>n2;
int n=0;
while(n<n1.size()){
cout<<((n1[n]-'0')^(n2[n]-'0'));
n++;
}
}
return 0;
}
//what is wrong or how to do more optimise for the given problem because all the testcase is not passing for me