97免费在线观看视频,亚洲综合自拍网,黄色毛片免费观看,热久久综合网,免费看日产一区二区三区 狠狠操av,久久久涩涩涩,在线精品免费视频,人人插天天干,久久91精品国产91久久

單項選擇題

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

微信掃碼免費搜題