单项选择题
A.Both seamless mild steel and copper may be used for middle pressure steam
B."hpair" means high pressure air
C.The feed piping of the boilers can be made of seamless mild steel
D.All oil pipings are made of mild steel
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 （）.
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 （）.