using System;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        string input = "ab";

​

        Match m1 = Regex.Match(input, "a()b");

        Match m2 = Regex.Match(input, "a()+?b");

        Match m3 = Regex.Match(input, "a(){1,}?b");

        Match m4 = Regex.Match(input, "a()*?b");

        Match m5 = Regex.Match(input, "a(){0,}?b");

        Match m6 = Regex.Match(input, "a()+b");

        Match m7 = Regex.Match(input, "a()*b");

​

​

        Console.WriteLine($"{m1.Success} {m1.Value}");

        Console.WriteLine($"{m2.Success} {m2.Value}");

        Console.WriteLine($"{m3.Success} {m3.Value}");

        Console.WriteLine($"{m4.Success} {m4.Value}");

        Console.WriteLine($"{m5.Success} {m5.Value}");

        Console.WriteLine($"{m6.Success} {m6.Value}");

        Console.WriteLine($"{m7.Success} {m7.Value}");

    }

}

​