单项选择题
An advantage of an ABC dry chemical over a carbon dioxide extinguisher is（）.
A.lack of toxicity B.the multipurpose extinguishing ability C.burn-back protection D.cooling ability
单项选择题 After using a Halon extinguisher，it should be（）.
单项选择题 After using a C02 portable extinguisher，it should be（）.
单项选择题 Accumulations of oily rags should be（）.
