1. [单选题]活塞环黏着在环槽中将导致______。
A. 密封不良
B. 弹力下降
C. 搭口间隙变小
D. 折断
2. [单选题]If a reciprocating air compressor has a knock occurring in frequency with its operating RPM, the cause is probably _____.
A. misalignment or worn main bearings
B. insufficient cylinder lubrication
C. defective or poorly fitted valves
D. All of the above
3. [单选题]在火场进行防护时，应做到以下几点：
A. 切断电源、油路
B. 隔离危险品
C. 冷却火场周围空间
D. 以上都是
