单项选择题
The bypass valve on a self-contained breathing device should be opened if（）.
A.you are entering a space containing poisonous vapors B.you are entering a space containing explosive gases C.the regulator of the breathing apparatus malfunctions D.the face piece of the breathing device is too tight
单项选择题 The boat is stowed on the davit rather than on a cradle with which type of davit?（）
单项选择题 Static electricity may be built up by the（）.
单项选择题 Permission is kindly requested（）the ballast water.
