单项选择题
Since accumulations of H2S gas on a ship can be dangerous to personnel，it is important to know that H2S gas is（）.
A.lighter than air B.heavier than air C.a yellow gas that is easily recognized D.mildly toxic
单项选择题 Severe exposure to chlorine gas can be fatal. Chlorine gas is primarily a（）.
单项选择题 Segregation of cargoes refers to（）.
单项选择题 Radiotelegrams requesting medical advice should state briefly and clearly the symptoms of the illness of the person（）.
