单项选择题
A tank has been sealed and unventilated for a long period of timeWhich of the following conditions does this indicate?（）
A.The tank is safe to enter B.The tank is especially dangerous to enter C.Carbon monoxide is present D.Water vapor present when the tank was sealed has oxidized
单项选择题 Fires occurring in combustible metals, such as sodium or magnesium, are classified as a （）.
单项选择题 A tank which has been sealed for a long period of time can be dangerous because （）.
单项选择题 Records of garbage disposal are required to be maintained （）.
