空气压缩机入口过滤器为何堵塞？
参考答案：
空气过滤器冬季结冻或积垢造成堵塞，使进气阻力增大，影响进气量，应进行定期检查和清洗。
_____ in the queue for half an hour, Tom suddenly realized that he had left his wallet at home. [ ]
A. To wait
B. Have waited
C. Having waited
D. To have waited
水泵内发生噼噼啪啪声响，可能是（）引起的。
A.泵倒转
B.汽蚀
C.弯轴
