测量氧气压力时，严禁压力表内有（），否则有爆炸危险。
A.水
B.油脂
C.空气
D.杂质
参考答案：B
— Hello, this is Tom. Is Jack in?
— Sorry, he _________to his uncle’s home. May I take a message?
A. has been B. go C. has gone
光学平直仪的测量范围为（）mm。
A.士0.2
B.士0.5
C.士1
D.士1.5
