题干

环己酮是一种重要的有机化工原料.实验室合成环己酮的反应如图1:

环己醇和环己酮的部分物理性质见下表:

物质

相对分子质量

沸点(℃)

密度(g•cm3、20℃)

溶解性

环己醇

100

161.1

0.9624

能溶于水和醚

环己酮

98

155.6

0.9478

微溶于水,能溶于醚

现以20mL环己醇与足量Na2Cr2O7和硫酸的混合液充分反应,制得主要含环己酮和水的粗产品,然后进行分离提纯.其主要步骤有(未排序):

a.蒸馏、除去乙醚后,收集151℃~156℃馏分

b.水层用乙醚(乙醚沸点34.6℃,易燃烧)萃取,萃取液并入有机层

c.过滤

d.往液体中加入NaCl固体至饱和,静置,分液

e.加入无水MgSO4固体,除去有机物中少量水

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根据短文内容, 从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

Improve your memory

    Some people often complain about their poor memory. Actually there are several ways to keep your memory sharp. This article will show you some simple tips.

    ____When you say these things, you begin to plant the thought in your mind and it may become true. Tell yourself you can remember anything as long as you put your mind to the task. You  will see an improvement in your memory.

    ____If you have trouble remembering phone numbers or other blocks of numbers, it can be really helpful to try this method. If you remember them in smaller groups, like two or three digits (数字), it will also be much easier to remember the numbers.

    Be sure to see a doctor if you are really losing your memory. A poor memory can be a sign that you are in low spirits.____

    Playing games also helps improve your memory. Any type of games that involves(涉及) remembering things is wonderful.____Try and remember it when you have nothing better to do. A useful tip for anyone interested in games is to often work on solving word puzzles and similar types of games.____

    Not only will your memory probably improve, but you will also have a great deal of fun.

A. Remember numbers in small groups.

B. Stop telling yourself you have a weak memory.

C. Take a right attitude.

D. If you don't like games, you can go over a list of "to do things".

E. If so, treating it could be the key to getting your memory back.

F. If you don't know your condition, you cannot treat it!

G. Such games use the same skills needed to remember facts and help keep the mind sharp.