單項(xiàng)選擇題Cast iron and gunmetal fittings are used freely in small sizes at moderate pressure; large fittings, those for high pressure and temperature are cast or mild steelIn the above sentence, the word “those” means （）.

A.east iron firings
B.mild steel fittings
C.small fittings
D.large fittings


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1.單項(xiàng)選擇題Wrought iron has an inherent resistance to corrosion but is not to be had freely , its place has been taken by the cuprous alloysAccording to the above sentence , which of the following statements is true?（）

A.Wrought iron can resist liquids flow
B.It is difficult to attain the wrought iron
C.Wrought iron should be combined with cuprous alloys
D.The cuprous alloys have mere disadvantages than wrought iron

2.單項(xiàng)選擇題Seamless mild steel is used for steam (also copper for moderate pressure and temperature), h-pair, feed discharge and all oil fuel pressure pipingsAccording to the above sentence, which of the following statements is not true?（）

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

3.單項(xiàng)選擇題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

4.單項(xiàng)選擇題"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

5.單項(xiàng)選擇題The soda-acid portable extinguishers must be discharged and refilled （）.

A.every six months
B.every year
C.every one and half year
D.every two years