利用小气量的控制气做控制，使气动装置动作的部件是（）。
A.继气器
B.继电器
C.油水分离器
D.单向阀
参考答案：A
.Since I came here two years ago, great changes __________ in the factory and many people want to come here to pay a visit.
A have been taken place B. had been taken place C. have taken place D. are taking place
教育学是研究_____________、揭示教育规律的一门科学。
