正则表达式C#来自特定字母列表的随机字母

using System;
using System.Text.RegularExpressions;

public class RandomLetterGenerator
{
    private static readonly Random random = new Random();

    public static char GenerateRandomLetter(string letterList)
    {
        Regex regex = new Regex($"[{letterList}]");
        string randomLetter = regex.Match(letterList[random.Next(letterList.Length)].ToString()).Value;
        return randomLetter[0];
    }
}

public class Program
{
    public static void Main(string[] args)
    {
        string letterList = "abc";
        char randomLetter = RandomLetterGenerator.GenerateRandomLetter(letterList);
        Console.WriteLine(randomLetter);
    }
}