问题
单项选择题
下列溶剂中哪个是最常用的制备格氏试剂的溶剂醚，哪个不能用于制备格氏试剂（）。
A.苯；
B.醚；
C.正己烷；
D.丙酮
答案
参考答案：D
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下列溶剂中哪个是最常用的制备格氏试剂的溶剂醚，哪个不能用于制备格氏试剂（）。
A.苯；
B.醚；
C.正己烷；
D.丙酮
参考答案：D
You have often __1__ people talk about work. Perhaps you have __2__ your friends about how hard you worked to get something done. However, you may have done no work __3_ you think you worked hard. A boy is pushing a big box very hard, but the box is __4__ heavy for him to move and he may __5__ to push against the box. __6__ the language of science, he has not done __7__ work. Can you think you are working when you are studying or talking? In science, work is only done when a force(力) moves something that has weight through a distance（距离）. Work =" force" × distance moved. __8_ you want to find out whether work is done, _9_ yourself, “Is a push or a pull moving something through a distance?” If your answer is __10_, then work is being done.
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