How to change one comboBox Items based on selection in another comboBox Item.

In this article iam going to explain how to change the combobox items on selection of another combobox.
Basically their are so many ways to solve this problem. but in this iam used simple way. I think it may be
helpful for beginners.
Drag and drop two Comboxes in windows form:

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;

namespace droupdown
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            
        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (comboBox1.SelectedItem == "B.Tech")
            {
                comboBox2.Items.Add("IT");
                comboBox2.Items.Add("CSE");

            }
            else if (comboBox1.SelectedItem == "PG")
            {
                comboBox2.Items.Clear();
                comboBox2.Items.Add("MCA");
                comboBox2.Items.Add("MBA");
            }
            else
            {
                MessageBox.Show("select item");
            }
        }
    }
}

In this i took very less Items so it will work but what about for large number of items…? I will give solution for that one in ASP.Net. Thank You.