import java.util.*;
import java.io.*;

public class usernames_verf {

	public static void main(String[] args) throws FileNotFoundException{
		Scanner scan = new Scanner(new File("usernames.input.txt"));
		PrintWriter out = new PrintWriter(new File("usernames.out"));
		int t = scan.nextInt();
		for(int q = 1; q <= t; q++){
			int n = scan.nextInt();
			if(!(n >= 3 && n <= 20)){
				problem(q);
			}
			String[] str = new String[n];
			for(int i = 0; i < n; i++){
				str[i] = scan.next();
				if(!isUppercase(str[i].charAt(0))) problem(q);
				if(i < 2 && str[i].length() < 2) problem(q);
			}

			String ans = str[0]+str[1].substring(0, 2)+"_";
			for(int i = 2; i < n; i++) ans += str[i].charAt(0);
			out.println(ans);
		}
		out.flush();
	}

	static boolean isUppercase(char c){
		return c <= 'Z' && c >= 'A';
	}

	static void problem(int caseID){
		System.out.println("Issue with case "+caseID);
	}
}