The regular expressions engine works from left to right by default, so only the left-most match is returned.
You can use the NextMatch method to return more matches:
using System;
using System.Text.RegularExpressions;
class Program
{
static void Main(string[] args)
{
Match m1 = Regex.Match("This is a test from rntsoft.com", @"2?s?");
Match m2 = m1.NextMatch();
Console.WriteLine(m1);
Console.WriteLine(m2);
}
}