如何在 C# 中添加 3 秒延迟 (Visual Studio 2010)

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 WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        int randumnum1;
        public Form1()
        {           
            InitializeComponent();          
        }
        public int randumnum()
        {
            Random r = new Random();
            int randumnum = r.Next(15, 30);
            return randumnum;
        }
        private void button2_Click(object sender, EventArgs e)
        {
         randumnum1 = randumnum();
         string strrandumnum = randumnum1.ToString();
         label4.Text = strrandumnum;        
         button2.Text = "New Game";       
        }      
        private void button1_Click(object sender, EventArgs e)
        {
            Random r = new Random();
            int computer = r.Next(1, 4);
            String strrandumnum;            
            if (((Convert.ToInt32(textBox1.Text)) < 1) || ((Convert.ToInt32(textBox1.Text)) > 3))
            {
                MessageBox.Show("Invalid input. Remember you can enter numbers between 1 and 3 only", "Error");
                textBox1.Text = "";
            }
            else if  (Convert.ToInt32(textBox1.Text) == 1)
            {   randumnum1 -= 1;
                strrandumnum = randumnum1.ToString();
                label4.Text = strrandumnum;
                textBox1.Text = "";
            }
            else if (Convert.ToInt32(textBox1.Text) == 2)
            {
                randumnum1 -= 2;
                strrandumnum = randumnum1.ToString();
                label4.Text = strrandumnum;
                textBox1.Text = "";
            }
            else if (Convert.ToInt32(textBox1.Text) == 3)
            {
                randumnum1 -= 3;
                strrandumnum = randumnum1.ToString();
                label4.Text = strrandumnum;
                textBox1.Text = "";
            }    
           //I want a 3 second delay right here but nothing seems to work. I tried the
           //thread sleep but it skipped all the other if statements and was messed up.
                randumnum1 -= computer;
                strrandumnum = randumnum1.ToString();
                label4.Text = strrandumnum;
              }