单项选择题
A.cannot be made with salt water
B.is heavier than oil and sinks below its surface
C.is corrosive and a hazard to fire fighters
D.conducts electricity
单项选择题 One disadvantage of using regular dry chemical (sodium bicarbonate) in firefighting is that（）.
单项选择题 One advantage of the all-purpose nozzle is that it（）.
单项选择题 Once a vessel has loaded packaged hazardous cargo，the cargo spaces shall be inspected. The spaces shall also be inspected at least once in every 24 hours. The only exception to daily inspection is when（）.