单项选择题 The vapors given off by heated fuel oil are heavier than air and are（）.

单项选择题 If it becomes necessary to pump bilges while a vessel is in port, which of the following procedures should be followed?（）

单项选择题 You are about to enter a compartment to investigate a suspected smoldering fireIf youre not wearing a self-contained breathing apparatus, you should test the compartments atmosphere to determine if there is/are （）.