#include
#include
using namespace std;
int main() {
int t,p=0;
cin>>t;
while(p<t)
{
string s1;
string s2;
cin>>s1>>s2;
vector v;
int size=s1.length();
for(int i=0;i< size;i++)
{
if(s1[i]==s2[i])
{
v.push_back(0);
}
else
{
v.push_back(1);
}
}
int end= v.size();
for(int i=0;i<end;i++){
cout<<v[i];
}
p++;
}
return 0;
}
