B选线省略了proportion，应为a greater proportion than （proportion）in any previous election。
Ron：there's ellipsis here. the understood comparison is a repeated instance of "proportion".
in contexts in which you would repeat a noun, you don't have to include the repeated noun; you may merely imply it. this is known as ellipsis.

for instance:
this year's heavyweight champion is shorter than last year's.
here, the second half of the comparison is clearly "last year's heavyweight champion", but you don't have to say "heavyweight champion" again.

than是作为比较代词的存在，要在句子中代指一个成分，这里代指proportion。
More people hope to live in the countryside than used to 。 代主语people
Don’t give children more money than is necessary. 代主语 money
He often eats more than is good for his health.代主语food
Tom is taller than John is. 代表语tall
I have more money than you do. 代宾语money
Tom runs faster than John runs. 代状语fast
这里贴一个探讨than的用法的帖子。http://ask.yygrammar.com/q-23051.html

还有另外一个PREP例题
Only seven people this century have been killed by the great white shark, the man-eater of the movies—less than those killed by bee stings.
A movies—less than those
B movies—fewer than have been
C movies, which is less than those
D movies, a number lower than the people
E movies, fewer than the ones

正确答案B中也省略了主语people。应为 seven people have been killed by the shark —fewer than（the people） have been killed by bee stings

than 之前的 句子里没有出现任何be动词可以比较的，所以有be的都错！！！！

第二次错！句子中没有出现be

than 之前的 句子里没有出现任何be动词可以比较的，所以有be的都错！！！！it和was出现得都不对

我理解B是省略，但不省略的话，应该是什么呢？a greater proportion than that was？

A选项什么叫少补语？具体少了什么

AC be动词，前面没有be动词可以放回，比较的对象
因此B选项比较对象是省略的Proportion,正确

than比较代词在句子里代指一个成分

比较的是proportion且前面没有Be

(C) "they" would have to refer to "soaring television costs", by elimination: there aren't any other plural nouns.

literally, this makes no sense, since television costs weren't "soaring" in OTHER elections.
(note that you MUST take the pronoun to stand for "soaring television costs"; you are NOT allowed to extract just "television costs" and pretend that the pronoun stands only for that.)

"have been" is an even bigger problem, though, since it implies the presence of "accounting". you can't do this unless the word "accounting" is actually present elsewhere in the sentence; it isn't.

actually, for those choices to make sense, "it" would have to be "proportion". (the proportion was greater in '92 than it was in any previous election.)

if "it/they" = "the cost(s)", then it's nonsense to use "was/were". you'd have to have "represented", "accounted for", "amounted to", etc.
'they have' or 'they did' can't make this option acceptable because "have"/"did" can't stand for "accounted for".

be动词，前后都要有

1.which修饰对象错误，DE错
2.代词指代，it和they的指代都不明确，而且不正确。
这里是比较和省略结合，把比较的名词省略掉。
a greater proportion than（the proportion）（television costs had accounted for of the spending）in any previous election

than 之前的 句子里没有出现任何be动词可以比较的，所以有be的都错！！！！

you can't use "were" in parallel to "accounted for".

a it was应改为they were
b 比较内容ratio of television costs in the spending in the presidential campaign 是同一个主体，随着时间的推移而变化，所以可以省略
c they have been应该改为they had been，因为是要和1992这个过去年份之前比较

a, it没有指代对象，前文出现的只有spending 和 campaign
且，就算不省略，也不能补be动词，前文是account for，应该补do

A it是完全指代

A：it doesn't stand for anything at all.

the only singular nouns that precede it are "spending" and "the presidential campaign of 1992". clearly, neither of these is an appropriate antecedent, so this choice is just wrong.

a greater proportion than（省略——前面出现过）

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