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【单选题】
注射模塑成型时的冷却阶段中,随着温度的迅速下降,型腔内的塑料体积收缩,压力下降,到开模时,型腔内压力不一定等于外界大气压力。型腔内压力与外界压力之差称残余压力,为了使脱模方便,塑件质量好。选择 ____________ 残余压力为好。A.
正
B.
零
C.
负
D.
都可以
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【简答题】Do you think that part-time jobs may help to build a sense of responsibility, which in tur n may enhance students' school performance? Give your reasons.
【判断题】Some people think part-time jobs help to build a sense of responsibility which in turn may enhance students' school performance.
A.
正确
B.
错误
【简答题】Do you think that part-time jobs may help to build a sense of responsibility, which in ture may enhance students' school performance? Give your reasons.
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