33. We were to go out for a walk ________ it began to rain.
A.while
B.before
C.as
D.when
答案:D
压缩空气管道安装完毕后,对其进行强度和严密性试验时的试验介质一般应为( )。
A.水
B.无油压缩空气
C.氮气
D.空气
Goodpasture综合征