#include
#include
using namespace std;
int main() {
int t;
cin>>t;
while(t–>0){
string a,b;
cin>>a>>b;
for(int i=0;i<a.length();i++){
if(a[i]=='1' and b[i]=='1' or a[i]=='0' and b[i]=='0'){
a[i]='0';
}else if(a[i]!=b[i]){
a[i]='1';
}
}for(int i=0;i<a.length();i++){
cout<<a[i];
}
}
return 0;
}