执行到foreach时报错："无效查询"，前面执行都过了，没问题，
代码如下：
...
try
{
System.Management.ObjectQuery oq = new System.Management.ObjectQuery("Win32_PerfRawData_PerfOS_Memory");
ManagementObjectSearcher mem = new ManagementObjectSearcher(scope,oq);
foreach( ManagementObject mo in q1)
{
this.textBox3.Text +=mo["AvailableMBytes"].ToString()+"; ";
Application.DoEvents();
}
}catch(Exception ex)
{
MessageBox.Show(ex.Message);
}