沙丁胺醇的作用机制是（）
A.兴奋β2受体
B.阻断M受体
C.阻断H受体
D.抗组胺
E.抑制磷酸二酯酶
参考答案：A
人员在()时，可以进入工作岗位进行维修、保养电梯。
A.睡眠严重不足
B.酗酒后未完全清醒
C.精神受刺激
D.身心状况良好
_____, we need to improve the equipment in our factory. [ ]
A. As it is
B. As it was
C. As it were
D. As it will be
