一段获取硬盘序列号的代码，错哪了

一段获取硬盘序列号的代码，哪里错了

C# code

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;using System.Management;namespace 显示cpu信息{    public partial class Form1 : Form    {        public Form1()        {            InitializeComponent();        }        private void Form1_Load(object sender, EventArgs e)        {            ManagementObjectSearcher searcher = new ManagementObjectSearcher("select * from Win32_PhysicalMedia");            String strHardDiskID = null;            foreach (ManagementObject mo in searcher.Get()) {                strHardDiskID = mo["SerialNumber"].ToString().Trim()；                break;            }            textBox8.Text = strHardDiskID;        }           }}