单项选择题
"Cast iron has poor corrosion resistance to sea water, especially in the presence of bronzes" Implies（）.
A.east iron is a cheap material B.cast iron can pollute sea water C.cast iron has mere corrosive than bronzes to sea water D.cast iron is more corrosive to sea water when it meets with bronzes
单项选择题 The soda-acid portable extinguishers must be discharged and refilled （）.
单项选择题 Class C fires are best extinguished by （）.
单项选择题 Class B fires are best extinguished by smothering, i-e（）.
