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举一反三
【单选题】Passage 3 Questions 11 to 15 are based on the following passage: Scientists in India have invented a new way to produce electricity. Their invention does not get its power from oil, coal or other fuel...
A.
Because bullocks have long been used by Indian people
B.
Because bullocks walk slowly and are easy to control.
C.
Because there are few non-working bullocks in India
D.
Because there is not enough oil in India.
【多选题】下面关于无心磨床描述正确的是( )。
A.
工件自由放置于定位夹具中，磨削过程中工件中心不定。
B.
无心磨床既能加工没有台阶的光轴，也能加工锥面和阶梯轴的外圆柱表面。
C.
无心外圆磨时工件没有纵向进给运动。
D.
无心磨削过程中，要求工件的中心和两个轮的中心等高。