柴油发动机做功行程是由（），混合气燃烧膨胀完成的。
A、火花塞点火
B、高温高压，气体自行发火
C、压缩做功
D、活塞密封良好
参考答案：B
The city,________ by mountains and lakes,is so beautiful that they have decided to stay there for
another two days. [ ]
A. stood
B. connected
C. blocked
D. surrounded
滑轮组应有防止钢丝绳跳出轮槽的防护装置。
