vb.net - 使用 System.Management 对象

Question

我写了这个例程：

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

但我有这个错误：

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

我有这些导入集：

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

还有什么需要的吗？谢谢