单项选择题

A.The p5-570 is rack mounted but the p5-550 is not.
B.The p5-570 will provide more growth, but at a higher cost.
C.The p5-570 is 200-240 volt only and the p5-550 is 110 volt only.
D.The p5-570 needs a special feature to become a deskside machine.