Vb.net 使用系统管理对象

我写了这个程序：

Public Function LipPCIsOn() As String
  '  Return TimeSpan.FromMilliseconds(System.Environment.TickCount).ToString()
  Dim query As New SelectQuery("SELECT LastBootUpTime FROM Win32_OperatingSystem WHERE Primary='true'")
  Dim searcher = New ManagementObjectSearcher(query)

  Dim ret As String = ""
  Dim mo As ManagementObject
  For Each mo In searcher.Get()
     Dim dtBootTime As DateTime = ManagementDateTimeConverter.ToDateTime(mo.Properties("LastBootUpTime").Value.ToString())
     ret = (Now - dtBootTime).ToString()
  Next

  Return ret
End Function

但我有一个错误：

SelectQuery is not defined
ManagementObjectSearcher is not defined
ManagementObject is not defined

我设置了这些导入：

Imports System
Imports System.Management
Imports System.Security
Imports System.IO
Imports System.IO.File
Imports System.IO.FileStream
Imports System.Windows.Forms

还需要什么吗？

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谢谢

项目>添加参考>组件选项卡，勾选“系统管理”。谢谢，我已经注意到我的道歉