c#正则取一段数据请教

Question

string sInput = File.ReadAllText(@"C:\Users\myx\Desktop\Test.txt", Encoding.GetEncoding("GB2312"));           
            string begin_date = @"2014/01/16";
            string end_date=@"2014/01/17";
            //=
            foreach (Match m in Regex.Matches(sInput, string.Format(@"(?<=<td>)\d+(?=</td>[\s\S]*?<td>[^<>]*?{0}\s*?-\s*?[^<>]*?</td>)", begin_date, end_date)))
            {
                //8 1
                
            }