import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.Scanner;

// MacKenzie and Andreas

public class Driver {

	public static void main(String[] args) throws FileNotFoundException {
		Scanner in= new Scanner(new File("a.in"));
		PrintWriter out= new PrintWriter(new PrintWriter("a.out"));
		
		int iter=in.nextInt(); 
		char [] row1, row2;
		
		in.nextLine();
		
		while(iter>0){
			row1=in.nextLine().toCharArray();
			row2=in.nextLine().toCharArray();
	
			
			for(int i=0; i<row1.length; i++){
				row1[i]=downChar(row1[i]);
				//System.out.print(row1[i]);
			}
			//System.out.println("");
			for(int i=0; i<row2.length; i++){
				row2[i]=upChar(row2[i]);
				//System.out.print(row2[i]);
			}
			
			String result="";
			int index1=0, index2=0;
			while(index1<row1.length || index2<row2.length){
				if(index1<row1.length){
					result+=row1[index1];
					index1++;
				}
				if(index2<row2.length){
					result+=row2[index2];
					index2++;
				}
			}
			
			out.println(result);
			
			iter--;
		}
		
		in.close();
		out.close();
	}
	
	private static char upChar(char in){
		char out;
		if((int)in==126)
			out=(char)32;
		else out=(char)((int)in+1);
		
		return out;
	}
	
	private static char downChar(char in){
		char out;
		if((int)in==32)
			out=(char)126;
		else out=(char)((int)in-1);
		
		return out;
	}

}