#include<bits/stdc++.h>
using namespace std;
#define ll long long int
int main() {
ll t,i;
cin>>t;
while(t--)
{
string a,b;
cin>>a>>b;
bitset<100>b1(a);
bitset<100>b2(b);
b1=b1^b2;
//cout<<b1;
string res="";
for(i=0;i<max(a.length(),b.length());i++)
{
res+=to_string(b1.test(i));
}
reverse(res.begin(),res.end());
cout<<res;
}
return 0;
}