#include <bits/stdc++.h>

using namespace std;

int main()
{
	int t, n, hamming_sum, max_val;
	string X, Y, Z, tmp;
	
	cin >> t;
	assert(t >= 1 && t <= 3);
	
	while ( t-- ) {
		
		cin >> X >> Y;
		
		n = (int)X.size();
		
		assert(n == (int)Y.size());
		assert(n >= 1 && n <= 16);
		
		for ( int i = 0; i < n; i++ ) {
			assert(X[i] == 'W' || X[i] == 'B');
			assert(Y[i] == 'W' || Y[i] == 'B');
		}
		
		max_val = -1;
		
		//bit masking considers all the possibilities.
		for ( int i = 0; i < (1 << n); i++ ) {
			
			tmp = "", hamming_sum = 0;
			
			for ( int j = 0; j < n; j++ ) {
				
				if ( i & (1<< j) ) tmp.push_back('W');
				else tmp.push_back('B');

				hamming_sum += (tmp[j] != X[j]) + (tmp[j] != Y[j]);
			}
			
			if ( hamming_sum > max_val ) max_val = hamming_sum, Z = tmp;
			else if ( hamming_sum == max_val ) Z = min(Z, tmp);
		
		}
		
		cout << Z << endl;
		
	}
	return 0;
}