A customer wants to expand their current storage environment, but has floor space for only two machine frames or two racks. Their environment consists of IBM SAN Volume Controllers and IBM DS4000 systems. The DS4000 systems are at end of lease. The customer wants the maximum number of disks possible in two frames. Which of the following solutions is best for this customer?（）

A. add one SVC
B. install one DS8700
C. install one DS8800
D. install one XIV system