单项选择题
Cast irons weakness in tension and under shock loading limits its use to low pressure steam, air, oil and low speed water fittingsThe above sentence, most probably means （）.
A.cast iron has weakness B.cast iron can stand up shock loading C.cast iron fittings are only suitable in low pressure situation D.east iron fittings are not suitable in low pressure situation
单项选择题 "Cast iron has poor corrosion resistance to sea water, especially in the presence of bronzes" Implies（）.
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 （）.
