Speech Recognition Programming

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C#

I am trying to design following project which converts "Speech to text"

but it shows following runtime exception:

PlatformNotSupportedException was Unhandled
Speech Recognition is not available on this system. SAPI and Speech Recognition engines cannot be found.

Please suggest me some solution for it.

Code is as under:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Speech.Recognition;

namespace speech_Recognition
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>


    public partial class Window1 : Window
    {
        private SpeechRecognitionEngine _recognizer = new SpeechRecognitionEngine();

        public Window1()
        {
            InitializeComponent();
        }

        private void button_Rec_Click(object sender, RoutedEventArgs e)
        {
            _recognizer.SetInputToDefaultAudioDevice();
            _recognizer.LoadGrammar(new DictationGrammar());
            _recognizer.SpeechRecognized += new EventHandler<SpeechRecognizedEventArgs>(_recognizer_SpeechRecognized);
            _recognizer.RecognizeAsync(RecognizeMode.Multiple);
        }

        void _recognizer_SpeechRecognized(object sender, SpeechRecognizedEventArgs e)
        {
            foreach (RecognizedWordUnit word in e.Result.Words)
            {
                listBox_Results.Items.Add(word.Text);
            }
        }
    }
}

[Edited]Unchecked Ignore HTML tags and entities[/Edited]