单项选择题
A.as it warms up it becomes heavier than air
B.the way it reacts with sea water
C.the strong odor it produces
D.its low temperature causes frostbite or freezing
单项选择题 Name one major advantage of transporting gas under refrigeration.（）
单项选择题 LFG tank and pipeline maintenance should include（）.
单项选择题 It should be noted（）the use of synthetic mooring ropes able to produce sparks by their manipulation is absolutely forbidden on board petroleum tankers and LPG or LNG carriers，or any vessels carrying inflammable substances.