活塞式内燃机按活塞运动方式分为()内燃机。
A.往复活塞式内燃机和旋转活塞式
B.往复活塞式内燃机合三角转子活塞式
C.三角转子活塞式合旋转活塞式
参考答案:A
3500与400的和是多少?差是多少?
You could hear water pipes cracking _____ they _____ because of the cold. [ ]
A. when; burst
B. before; were burst
C. when; were burst
D. before; burst