How Do I Enable A Speech Recognition Event In Widows Form ?

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C#

C#4.0

hello,
i am working on a project called interactive ATM with the functionality of speech commands. i am stuck at a point where i speak a particular option but it does not redirect to that respective \ "option" window.the event in which the recognizer should redirect me to that windows is not firing. i am giving the code below, please help me out...
regards

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

namespace SpeechRec
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            SpeechRecognitionEngine _recognizer = new SpeechRecognitionEngine();

            InitializeComponent();
            panela.Visible=true;
            panelb.Visible = false;
            panelc.Visible = false;
            paneld.Visible = false;

            _recognizer = new SpeechRecognitionEngine();
            _recognizer.SetInputToDefaultAudioDevice();

            Choices commandChoices = new Choices("Services", "mini statement", "mobile registration");
            GrammarBuilder gb = new GrammarBuilder();
            gb.Append(commandChoices);
            Grammar g = new Grammar(gb);
            _recognizer.LoadGrammar(g);

            _recognizer.RecognizeAsync(RecognizeMode.Multiple);

            _recognizer.SpeechRecognized += (s, args) =>
                {
                    string line = "";
                   

                    string command = Regex.Replace(line,"start", "").Trim();

                    switch (command)
                    {

                        case "Services":
                            panelb.Visible = true;
                            panela.Visible = false;
                            
                            break;
                        case "mini statement":
                            panelc.Visible=true;
                            break;
                        case "mobile registration":
                            paneld.Visible = true;
                            break;
                            default:
                            break;
                    }
                   
                };

        }
        private void Form1_Load(object sender, EventArgs e)
        {

        }       
        private void button1_DoubleClick(object sender, EventArgs e)

        {
          
        }
       
        private void Button4_Click(object sender, EventArgs e)
        {
            
         }            
    }
}