立柱和前探梁千斤顶供液后不动作或伸出太慢可能造成的原因是（）。
A.活塞杆弯曲变形卡死
B.严重撞击
C.进回液管打折或堵塞
参考答案：A
Afraid ______ face before his students, the teacher refused ______ that he was in the wrong. [ ]
A. to lose; to admit
B. of losing; admitting
C. of losing; to admit
D. to lose; admitting
从有线电视系统天线引下的线缆应采用（）。
A.单屏蔽电缆
B.单屏蔽电缆穿金属管敷设
C.双屏蔽电缆
D.扁平电缆
