C#中的多行正则表达式

using System;
using System.Text.RegularExpressions;

public class Program
{
    public static void Main()
    {
        string input = "This is line 1.\nThis is line 2.\nThis is line 3.";
        string pattern = @"^This.*$";

        RegexOptions options = RegexOptions.Multiline;

        foreach (Match match in Regex.Matches(input, pattern, options))
        {
            Console.WriteLine(match.Value);
        }
    }
}

This is line 1.
This is line 2.
This is line 3.

This is line 1.
This is line 2.
This is line 3.

This is line 1.
This is line 2.
This is line 3.