using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;
using System.Linq;
public class Test
{
	public static void Main()
	{
		var strs = new List<string>() { "Boy has a dog and a cat.", 
			"Boy something a gerbil.",
			"Sally owns a cat." };
		foreach (var s in strs)
		{
			var results = Regex.Matches(s, @"(?<=^Boy\b.*?)\b(?:dog|cat|gerbil)\b")
		        .Cast<Match>()
		        .Select(m => m.Value)
		        .ToList();
		     if (results.Count > 0) {
			Console.WriteLine("{0}:\n[{1}]\n------", s, string.Join(", ", results));
		     }
		     else
		     {
		     	Console.WriteLine("{0}:\nNO MATCH!\n------", s);
		     }
		}
	}
}

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