这道题prep的讲解说的是A的比较对象不一致。用老师教的方法看是用 than 分开前后，把后面的句子补全。
A 就是 Today's technology allows manufacturers to make small cars more fuel-efficient at any time in their production history。所以这边错的是没有other？ 这样解释是对的吗？ 不知道是不是可以用 at any other time 直接排除 A 和B。

B 的they是同物指代，错误。应该用同类指代

A.B讲的是，今天的small cars比这批cars在其他时候更省油；
C讲的是，今天的small cars 比其他时候的cars更省油；
前者比较的是同一批车在不同时间的省油情况，后者比较的是不同时间的两批车的省油情况。另外B项个人觉得比较碍眼的是they和their的同源指代的问题；
D.E里more修饰歧义，修饰数量更多or更省油?

In general, the point of "that" and "those" is to stand for nouns without any attached modifiers/descriptions.
There's an explicit contrast with "it" and "they", which stand for a noun with all of the attached modifiers.

E.g.,
The government of Country X is more stable than it was two years ago.
"It" = "the government of country X"
It is impossible to use "it" to stand for government in general. In this context, "it" can refer only to the government of country X.

Vs.
The government of Country X is more stable than that of Country Y.
"That" = "the government". NOT the government of country X.

The whole point of comparisons, of course, is to compare two different things. So, these pronouns are extremely useful because they're designed to do exactly that-- to stand for only the parts that are actually the same.

A. 将small cars的now和at any time相比较，现在的小车和其他时候的该小车做比较，但应该将today's small cars和small cars at any other time做比较的。at any time并没有剔除掉Today的时间点。today和now重复
B. they指代的就是前面的small cars，还是将现在的该小车和其他时候的该小车做比较。at any time没有剔除掉today的时间点。they是同物指代，指代的就是前面出现的东西
C. right，those是同类指代，指代的是同类的small cars。
D. more fuel-efficient small cars有歧义，到底是更多的省油车还是更省油的车？their可能指代manufacturers也可能指代small cars
E. more fuel-efficient small cars有歧义，到底是更多的省油车还是更省油的车？at any time没有剔除today的时间点

Answer A suggests that the manufacturers are making small cars efficient, i.e. they're changing small cars, but in fact they're making small cars that are efficient.

I don't think that pronoun ambiguity is the criterion here.

the sentence is supposed to say that today's small cars are more fuel-efficient than previous small cars -- i.e., OTHER small cars.
this is important, because you can't use a "they"/"their" construction (which would illogically imply that you're talking about the same small cars mentioned in the first part of the sentence).
the use of "those" in (c), on the other hand, accomplishes this distinction nicely.

analogy:

sprinters in texas can run faster than they can in north dakota.
--> illogical; in this sentence, "they" would be taken to mean "sprinters in texas" (i.e., not just sprinters).

sprinters in texas can run faster than those in north dakota.
--> makes sense; "those" = sprinters, in this case.

same thing with "they/their" vs. "those" in these instances.

A选项的问题是比较对象不是一类，比较对象是now和at any time，现代科技能使小车”在现在比在过去”省油，语义存在逻辑错误；today和Now重复；at any time没有将自身排除在外，应为any other time
B选项的问题也是比较对象不是一类，比较的是small cars和they were。另外they是指上文提及的东西，放在这里变成谈及的small cars和这些cars在历史上的比较，显然语义也不正确
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I'm going to make air conditioners quieter. --> I'm going to modify existing air conditioners so that they make less noise.

I'm going to make quieter air conditioners.
I'm going to make air conditioners that are quieter.
--> I'm going to make a new model that makes less noise.

A is like the first one of these, so it doesn't make sense in context.

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首先排除DE，more fuel-efficient small cars有歧义，是“更多”的fuel-efficient small cars，还是“更节能”的small cars？
B they指代的是前面的small cars，是让同一批车子比之前更节能。排除
A 也是同一批small cars，“让车子现在比它们之前更节能”。排除
C that are more fuel-efficient than those at any other time in their production history是定语，修饰前面的small cars，意思是“能造出这样的小车，这些小车要比之前任何时候生产的小车更节能。”

1.句意推理，more fuel-efficient small cars意思是造更多车，重点在车上
small cars that are more fuel-efficient ，重点在更节能上，后者更符合句意。DE错
A的意思是造车的动作更节省油，A的句意更错，A错。
2.比较，平行，more..than...，AE对比的对象都不一致
B的than they were的were用错，ABE错。

A. 将small cars的now和at any time相比较，现在的小车和其他时候的该小车做比较，但应该将today's small cars和small cars at any other time做比较的。at any time并没有剔除掉Today的时间点。today和now重复
B. they指代的就是前面的small cars，还是将现在的该小车和其他时候的该小车做比较。at any time没有剔除掉today的时间点。they是同物指代，指代的就是前面出现的东西
C. right，those是同类指代，指代的是同类的small cars。
D. more fuel-efficient small cars有歧义，到底是更多的省油车还是更省油的车？their可能指代manufacturers也可能指代small cars
E. more fuel-efficient small cars有歧义，到底是更多的省油车还是更省油的车？at any time没有剔除today的时间点

at any time没有排除现在

A选项的问题是比较对象不是一类，比较对象是now和at any time，现代科技能使小车”在现在比在过去”省油，语义存在逻辑错误；today和Now重复；at any time没有将自身排除在外，应为any other time
B选项的问题也是比较对象不是一类，比较的是small cars和they were。另外they是指上文提及的东西，放在这里变成谈及的small cars和这些cars在历史上的比较，显然语义也不正确
D选项的问题是their的指代不清楚，their可以指的是前面的cars也可以是manufacturers
E选项的问题是比较对象不是一类，比较的是small cars和 time in history；另外前面的more+adj+daj有歧义，到底是更多的车，而这些车是经济省油的还是更经济省油的小车？

(D) and (E) change the meaning of the original sentence. Both imply that manufacturers are making a great number of fuel efficient cars, and not cars that are more fuel efficient. To illustrate, saying that you have increased the number of cars that get 50 km/gallon is different from saying that you now make more fuel efficient cars that can get. 60km/gallon.

A，make cars more efficient now than before=make cars more efficient now than they were before，意思是使得同一批小汽车现在比过去更有效率。

C，make cars more that are more efficient now than those before
生产的是不同的小汽车，比较的是不同小汽车的车的一个性质--燃油效率的高低，生产比之前的小汽车更具燃油效率的小汽车。
改成make small cars more fuel-efficient now than those before也是可以的

CD的more有修饰歧义，是”更fuel-efficent“的小轿车，还是”更多fuel-efficient的小轿车“

A.比较对象为small cars和in their history不可比；

B.they指代前面提到的相同的事物，但实际上比的是同类不同物，逻辑错误，且they were和small cars不可比；

C.对，比较对象可比；

D.their指代不清，可能指代manufacturer或者cars；

E.small cars和at any time不可比

a比较时间：now than at any time in history，是同物比较，同一批cars
b和c比较cars，区别在they和those，同理they是同物比较，those换了一批cars
d和e比较的是形容词更efficient

谁的production history，cars还是manufacturer？去掉了their就不模糊了吗？

E. more 是修饰efficient还是cars？
any other time is better than any time?

today和now意思有重复

A，make cars more efficient now than before=make cars more efficient now than they were before，意思是使得同一批小汽车现在比过去更有效率。

C，make cars more that are more efficient now than those before
生产的是不同的小汽车，比较的是不同小汽车的车的一个性质--燃油效率的高低，生产比之前的小汽车更具燃油效率的小汽车。
改成make small cars more fuel-efficient now than those before也是可以的