WinForm的ComboList

写了一个简单的省市级联,但是怎么让他默认选中第一项?using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;namespace Test3_1
{
    public partial class FirstForm : Form
    {
        public FirstForm()
        {
            InitializeComponent();
        }        private void cmbProvince_SelectionChangeCommitted(object sender, EventArgs e)
        {
            object[] jiangsu = {"苏州","无锡","常州"};
            object[] zhejiang = { "杭州", "温州", "绍兴"};
            object[] shandong = { "济南", "青岛"};            string strPro = this.cmbProvince.Text.Trim();
            //MessageBox.Show(strPro);            switch (strPro)
            {
                case "江苏":
                    this.cmbCity.Items.Clear();
                    this.cmbCity.Items.AddRange(jiangsu);
                    break;
                case "浙江":
                    this.cmbCity.Items.Clear();
                    this.cmbCity.Items.AddRange(zhejiang);
                    break;
                case "山东":
                    this.cmbCity.Items.Clear();
                    this.cmbCity.Items.AddRange(shandong);
                    break;
            }        }
    }
}