当前上下文中不存在名称“匹配”

I have this code:

我有这个代码:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
namespace RegexTest
{
    class Program
    {
        static void Main(string[] args)
        {
            string str = "The quick brown fox.";
            string pat = "fox";
            Regex rgx = new Regex(pat, RegexOptions.IgnoreCase);
            Match matches = rgx.Match(str);
            Console.ReadKey();
        }
    }
}
using System;
usi