By default， what is Driver Signing set to in Windows XP？（）

A.in all cases
B.for some non PnP（non plug and play） device drivers and all PnP（plug and play） device drivers
C.for all non PnP（non plug and play） device drivers and most PnP（plug and play） device drivers
D.not for any non PnP（non plug and play）device drivers,only for all PnP（plug and play） device drivers

A.open a command prompt and type DEFRAG
B.at Startup， press the <F8> key and select Defrag Disk
C.right-click My Computer， Manage， Disk Defragmenter
D.right-click Drive icon， Tools， Defragment Now

A.Windows XP Home
B.Windows XP Professional
C.Windows 2000 Professional
D.Windows NT 4.0