Eliminates duplicate values from combo box

Question

This is the actual code

 

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;

namespace WindowsFormsApp1

{

public partial class Form1 : Form

{

public Form1()

{

InitializeComponent();

}

private void timer1_Tick(object sender, EventArgs e)

{

comboBox1.Items.Add("Duplicate");

}

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)

{

}

private void Form1_Load(object sender, EventArgs e)

{

comboBox1.Items.RemoveAt();

timer1.Start();

}

}

}

 

 

can someone help me?