单项选择题
Atmospheres laden with coal dust or grain dust caused by loading these cargoes（）.
A.require loading operations to be shut down until the atmosphere clears B.are toxic to human life C.are subject to spontaneous combustion D.may be explosive in some concentrations
单项选择题 Antiseptics are used principally to（）.
单项选择题 An unconscious person should NOT be（）.
单项选择题 An advantage of an ABC dry chemical over a carbon dioxide extinguisher is（）.
