单项选择题
Regulations require that cargo pumprooms on tank barges (constructed in 1965) carrying grades B or C liquid cargoes have power ventilation systems which can completely change the air in （）.
A.1 minute B.3 minutes C.5 minutes D.10 minutes
单项选择题 Petroleum cargo tanks should not be topped off at deck level when loading on a cold day because（）.
单项选择题 One of the principal dangers inherent in liquefied petroleum gas is（）.
单项选择题 Inerting means（）.
