YouhaveacomputerthatrunsWindowsVista.Thecomputerhasonepartitionand1GBofRAM.YouneedtoupgradethecomputertoWindows7.Whatshouldyoudofirst?()

A.Add1GBofRAM.

B.Createasecondpartition.

C.DisableUserAccountControl（UAC）.

D.InstallWindowsVistaServicePack2（SP2）.