“全浮式”活塞销在发动机工作时，可以在（）内缓慢地转动。
A.连杆小端衬套孔
B.活塞销座孔
C.连杆小端衬套孔和活塞销座孔
参考答案：C
Many rivers ________. [ ]
A. have became polluted
B. have become polluted
C. have been polluting
D. have become polluting
活塞式制冷压缩机油温应保持在（）度之间。
A.20-40
B.40-60
C.60-80
D.80-100
