CODE

#include<iostream>
#include<string>
#include<bits/stdc++.h>
using namespace std;

int main ()
{
    int i ;
    char input1[1000000] ;
    cin>>i;
    while(i--)
    {
        cin>>input1;
        int n = strlen(input1);
        char input2[n];
        cin>>input2;
        for(int j=0; input1[j]!='\0'; j++)
        {
            if(input1[j]=='W'&&input2[j]=='W')
            {
                cout<<"B";
            }
            else if (input1[j]=='B'&&input2[j]=='B')
                cout<<"W";
            else cout<<"B";
        }
        cout<<endl;
    }

    return 0;
}