using System;
using System.Collections.Generic;
using System.Linq;

public class Test
{
	public static void Main()
	{
		var A = new[] {"1","2","3"};

		var B = new[] {
			"1,2,3,4,5,6,7",
			"1,2,6,7",
			"1",
			"4,5,6",
			"6,7"
		};
			
		var matches = B.Where(s => s.Split(',').Intersect(A).Any()).ToList();
		foreach(var match in matches) Console.WriteLine(match);
    
	}
}