The class ________seven groups, each having eight students. [ ]

A. divides into    

B. is divided into

C. separates from  

D. is separated from

螺杆压缩机不需设置（），而由（）位置来控制其在工作腔内所能达到的压力。因此螺杆压缩机压力比有内压力比和外压力比之分。