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【多选题】
芯头有哪些要求( )。A.
定位和固定砂芯,使砂芯在铸造中有准确的位置,并能承受砂芯重力及浇注时液体金属对砂芯的浮力,使之不破坏
B.
芯头应能及时排出浇注后砂芯所产生的气体至型外
C.
上下芯头及芯号容易识别,不致下错方向或芯号
D.
下芯、合型方便,芯头应有适当斜度和间隙
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举一反三
【单选题】Assuming that the engineering problems could be overcome, the production of a time machine could open up a Pandora's box of causal paradoxes. Consider, for example, the time traveler who visits the pa...
A.
the time machine in the future would be feasible
B.
the time machine in the future is just like the Pandora's ox
C.
the time machine in the future is still doubtful
D.
the time machine in the future might cause murder
【单选题】The old couple walked rather slowly, and could be seen, from time to time, to stop and rest, ________ out to sea.
A.
to be staring
B.
stared
C.
having stared
D.
staring
【单选题】The young man spent as much time as he __ over his lessons.
A.
went
B.
could go
C.
could going
D.
could to go
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