Your company has an Active Directory Domain Services (AD DS) domain that runs at the Windows Server 2008 functional level. All servers run Windows Server 2008 R2. All client computers run Windows XP Professional. You use the Key Management Service (KMS) to manage your volume license activations. All servers have been activated by using KMS. You deploy 20 Windows 7 virtual desktops. The virtual desktop operating systems do not activate. You need to ensure that the virtual desktops activate by using KMS. What should you do?（）

A. Deploy five more virtual desktops.
B. Run slmgr.vbs with the -ato parameter.
C. Use the Volume Activation Management Tool (VAMT).
D. Raise the domain functional level to Windows Server 2008 R2.