1. [单选题]四冲程柴油机活塞触火面裂纹主要发生在_______处
A. 活塞顶面
B. 环槽根部
C. 活塞销座附近
D. 裙部
2. [单选题]When checking zinc plates in the refrigerating system condenser, you should
A. paint and insulate the plates to prevent corrosion
B. renew the plates at each inspection
C. replace the zincs if deteriorated by 50%
D. file the plates to change the negative value
