储压式呼吸器的作用是用来净化空气的.
参考答案:对
对维生素B12的正确描述:
A.维生素K拮抗剂
B.口服可吸收
C.二者均可
D.二者均不可
.It would ______us a ____ time, but fortunately, we didn’t.
A.take; along
B.take; longer
C.have taken; longer
D.have taken; long