--- Look! The paint is starting to come off _______ the wall is damp.

--- Well, we’d better have the wall repainted some day.[ ]

A. when

B. where

C. if

D. once

离心式压缩机的启动程序不包括（）。

A.启动油泵，检查并调整各处油压

B.启动压缩机

C.调整导叶

D.调整压缩机排气阀