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举一反三
【单选题】In many places water is becoming scarcer. Treating it as a right makes the scarcity worse. Ideally, efficient water use would be encouraged by charging for it, but attempts to do so have mostly proved...
A.
People should only be entitled to certain amount of water free.
B.
People can borrow water from their neighbors when necessary.
C.
People are free to bargain for water in market in their daily lives.
D.
People have the right to trade water to raise water productivity.
【单选题】加速器的等中心是指（）
A.
机架的旋转中心与束流中心一致
B.
机架的旋转中心与小机头旋转中心一致
C.
机架的旋转中心与治疗床的旋转中心相一致
D.
机架的旋转中心、束流中心与治疗床旋转中心一致
E.
机架的旋转中心、小机头旋转中心、治疗床旋转中心与束流中心相一致