单项选择题
A tank which has been sealed for a long period of time can be dangerous because （）.
A.steel surfaces consume oxygen by rusting B.sealed tanks usually form a vacuum C.moisture condenses in the tank, displacing the oxygen D.most tank coatings give off poisonous vapors in the presence of moisture
单项选择题 Records of garbage disposal are required to be maintained （）.
单项选择题 The use of sinking and dispersing agents for the removal of surface oil is （）.
单项选择题 One of the disadvantages of using carbon dioxide to extinguish a fire in an enclosed space is （）.
