单项选择题
A carbon dioxide fire extinguisher should be recharged（）.
A.at least annually B.whenever it is below its required weight C.only if the extinguisher has been used D.before every safety inspection
单项选择题 A certificated lifeboatman assigned to command the lifeboat must（）.
单项选择题 A chain stripper is used to（）.
单项选择题 A check line is（）.
