Two strings - Hashset - overlaps - code is readable.

TwoStrings7.cs

using System;
using System.Collections.Generic;

class Solution
{
    static void Main(String[] args)
    {
        var t = Convert.ToInt32(Console.ReadLine());
        var stringsA = new string[t];
        var stringsB = new string[t];

        for (var i = 0; i < t; i++)
        {
            stringsA[i] = Console.ReadLine();
            stringsB[i] = Console.ReadLine();
        };

        for (var i = 0; i < t; i++)
        {
            var hasCommon = false;
            var set = new HashSet<char>();
            for (int j = 0; j < stringsA[i].Length; j++)
            {                
                set.Add(stringsA[i][j]);
            }

            

            for (int j = 0; j < set.Count; j++)
            {
                hasCommon = set.Overlaps(stringsB[i].ToCharArray());
                if (hasCommon) break;
            }

            Console.WriteLine(hasCommon ? "YES" : "NO");
        };
    }
}