氧气混合站开车过程中，不需要复位打开的阀门是（）。
A、氧气进料阀
B、乙烯进料阀
C、甲烷进料阀
D、抑制剂进料阀
参考答案：A
---When did you move to Beijing? ---Last year. But I _____ in a school in Japan for 8 years.
A．has taught
B．taught
C．has been taught
D．has been teaching
第二类杠杆又称为（）
A.平衡杠杆
B.省力杠杆
C.速度杠杆
D.静态杠杆
E.费力杠杆
