基于C#进行界面设计时,如何实现ComboBox和ListBox的功能

    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 ComboListBox
    {
    public partial class Form1 : Form
    {
        public Form1( )
        {
            InitializeComponent( );
        }
    
        private void Form1_Load(object sender, EventArgs e)
        {
            //