C# - how to do multiple web requests at the same time

I wrote a code to check urls, however, ir works really slow.. I want to try to make it work on few urls at the same time, for example 10 urls or at least make it as fast as possible.

I know you will probably say, you have 10 cores and that parallel desicions, but there must be a way to make it much faster. I know tools that check 50 urls in 1 second, how they do it? how can I do it?

my Code:

Parallel.ForEach(urls, new ParallelOptions { MaxDegreeOfParallelism = 10 }, s =>
        {
            try
            {
                using (HttpRequest httpRequest = new HttpRequest())
                {
                    httpRequest.UserAgent = "Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Firefox/52.0";
                    httpRequest.Cookies = new CookieDictionary(false);
                    httpRequest.ConnectTimeout = 10000;
                    httpRequest.ReadWriteTimeout = 10000;
                    httpRequest.KeepAlive = true;
                    httpRequest.IgnoreProtocolErrors = true;
                    string check = httpRequest.Get(s + "'", null).ToString();
                    if (errors.Any(new Func<string, bool>(check.Contains)))
                    {
                        Valid.Add(s);
                        Console.WriteLine(s);
                        File.WriteAllLines(Environment.CurrentDirectory + "/Good.txt", Valid);
                    }
                }
            }
            catch
            {

            }
         });