get current word high-lighted by reading SpeaksAsync method

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C#

Dear All,
I need solution for making current word high-lighted being read by SpeackAsync method.
Example:-Robin is a good boy.

in this if SpeakAsync reading at is then is should be highlight.

Plz look at given coding,,,,,,,

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Speech.Synthesis;
using System.IO;
namespace text_to_speech
{
    public partial class Form1 : Form
    {
        SpeechSynthesizer reader;
        public Form1()
        {
            InitializeComponent();
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            reader = new SpeechSynthesizer();
            btnPause.Enabled = false;
            btnResume.Enabled = false;
            btnStop.Enabled = false;
            xtxtContent.ScrollBars = ScrollBars.Both;
            
            volumebar.Maximum = 100;
            speedbar.Maximum = 10;
            speedbar.Minimum = -5;
            volumebar.Value = 50;
           
        }
        //SPEAK TEXT
        private void button1_Click(object sender, EventArgs e)
        {
            reader.Dispose();
            if (xtxtContent.Text != "")
            {
                reader = new SpeechSynthesizer();
                reader.Volume = volumebar.Value;
                reader.Rate = speedbar.Value;
                
                reader.SpeakAsync(xtxtContent.Text);
                label2.Text = "SPEAKING";
                btnPause.Enabled = true;
                btnStop.Enabled = true;
                reader.SpeakCompleted += new EventHandler<SpeakCompletedEventArgs>(reader_SpeakCompleted);
            }
            else
            {
                MessageBox.Show("Please enter some text in the textbox", "Message", MessageBoxButtons.OK);
            }
        }
        void reader_SpeakCompleted(object sender, SpeakCompletedEventArgs e)
        {
            label2.Text = "IDLE";
        }

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