using System;
using System.IO;
using System.Text.RegularExpressions;
using System.Linq;
public class Test
{
	public static void Main()
	{
		var text = "there are big widgets in this phrase blue widgets too";
		var words = "big blue widgets";
		var pattern = $@"(\s*(?<!\w)(?:{string.Join("|", words.Split(' ').Select(Regex.Escape))})(?!\w)\s*)";
		string result = string.Concat(Regex.Split(text, pattern, RegexOptions.IgnoreCase).Select((str, index) =>
                index % 2 == 0 && !string.IsNullOrWhiteSpace(str) ? $"<b>{str}</b>" : str));
        Console.WriteLine(result);
	}
 
 
}
 
 

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