题目

So experienced a guide _____that we finally walked out of the thick forest. A. we had   B. did we have C. had we      D. we did have 答案：B15．某单缸四冲程汽油机的转速是600R/min，则下列说法正确的是（　　）A．1min内燃机对外做了600次功B．1s内完成了10个工作循环C．燃气做一次功的时间间隔是0.2sD．1s内活塞共来回20次