Problemă loop c# Visual Studio

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Speech.Synthesis;
using System.Speech.Recognition;
using System.Diagnostics;

namespace Command
{
	public partial class Speech : Form
	{
		SpeechSynthesizer s = new SpeechSynthesizer();
		public Speech()
		{
			InitializeComponent();
			SpeechRecognitionEngine reco = new SpeechRecognitionEngine();
			Choices list = new Choices();
			list.Add(new string[] { "hi" , "hello"});
			Grammar gm = new Grammar(new GrammarBuilder(list));

			try
			{
				reco.RequestRecognizerUpdate();
				reco.LoadGrammar(gm);
				reco.SpeechRecognized += Reco_SpeechRecognized;
				reco.SetInputToDefaultAudioDevice();
				reco.RecognizeAsync(RecognizeMode.Multiple);
			}
			catch { }
		}

		private void Reco_SpeechRecognized(object sender, SpeechRecognizedEventArgs e)
		{
			string a = e.Result.Text;

			switch (a)
			{
				case ("hello"):
						{
						s.SpeakAsync("opening google");
						Process.Start("[url="https://www.google.com"]https://www.google.com"[/url]);
						break;
						}
				case ("hi"):
						{
						s.SpeakAsync("hi");
						break;
						}		
			}
		  
		}
	}
}