多行C#正则表达式匹配空行后

string pattern = @"^\s*$";

using System;
using System.Text.RegularExpressions;

class Program
{
    static void Main(string[] args)
    {
        string input = "This is a test.\n\nAnother test.\n";
        string pattern = @"^\s*$";
        RegexOptions options = RegexOptions.Multiline;

        foreach (Match match in Regex.Matches(input, pattern, options))
        {
            Console.WriteLine("Empty line found at position {0}", match.Index);
        }
    }
}

Empty line found at position 11
Empty line found at position 23