引用：
1、prevent somebody/something (from) doing something 这里from 是可以省略的，如：Wrap eggs in paper to prevent them being damaged，来自朗文例句。所以DE的问题应该还是在aim to上，个人认为至少E的形式没有问题；
2、翻了些词典，aim 大体有三个意思，刚好aim at都适用这三种意思：（1）指向，aim a camera at me（镜头对准我），（2）针对（特定人群或事物），These ads are aimed at young people（这些广告是针对年轻人的）；（3）to plan, hope, or intend to achieve something，力求达到/旨在。显然这里的aim to和aim at 都属于第3个意思，用法分别为：aim to do sth和aim at doing sth，但有细微区别的是aim to do的动作发起人一般为人或机构，如I aim to be a millionaire by the time I'm 35 字面翻译为“力求达到”，aim at sth/doing sth动作发起方是计划、方案等事物 ，如The talks are aiming at a compromise 字面翻译为“旨在于……” 所以这里医保法案用aim at 不用aim to
句子主干是slackening is inflluenced less by gov reg than by
by the coming to an end of 和by the end of 对句子理解有很大影响，by the coming to an end of a period是指时期将要结束（时期还没结束），一个持续性过程，by the end of a period 指时期结束，一个时间点。
D的错误在于，不平行，一个动作无法与之前的名词平行
积累the coming to an end 即将结束
the coming to an end of...即将结束的...
1.key takeaway
X is 200 times as old as Y -- CORRECT.
X is 200 years as old as Y -- WRONG.
X is 200 years older than Y--CORRECT
2.supposed修饰predecessors，表示推测可能是predecessors，
supposedly是副词不修饰predecessors，而是修饰Mediterranean，地中海地区的。
it is hoped 表客观，ETS prefer
hopefully 表主观，GMAT中一般为错误选项
hopefully meaning "i hope that/let's hope that". This is an informal expression, and is generally avoided in writing.
gravity waves 不会interact with matter，
B correct
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积累：
extent of表示 ...的范围
to ..extent 表示 程度
etc. to what extent you can accept the fact
（没有extent to的表达 )
the degree to sth 或者to…degree, 表示…的程度