- using System; 
- using System.Text.RegularExpressions; 
-   
- public class Test 
- { 
- 	public static void Main() 
- 	{ 
- var pattern = "hello % world _"; 
- var escapedPattern = Regex.Replace(pattern, "[%_]", "_$0"); 
- Console.WriteLine(escapedPattern); 
- 	} 
- } 
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