抽氟完毕后,停抽氟机之前应关闭的阀门是()。
A、吸气阀
B、排气阀
C、加氟阀
D、冷凝器放空阀
参考答案:D
You are getting closer to the vessel(),which is on the same course as you.
A.head
B.ahead
C.headed
D.heading