To develop more accurate population forecasts, demographers have to know a great deal more than now about the social and economic determinants of fertility.
(A) a great deal与now比较(than后面只有一个成分now，所以a great deal只有与其进行对比)，概念不对等。
(B) economic的意思是：relating to trade, industry, and the management of money，而economical为便宜or节省的意思，根据逻辑含义应该用economic。
(E) a great deal与now比较，概念不对等 。
RON大神的解析 don't forget the difference between "economic" and "economical", which is huge. "economic" means "having to do with "economics and/or the economy". (this is the intended meaning.) "economical" means "efficient" or "at low cost/expense". (this is not the intended meaning.) i think this sentence makes sense with either "would have to" or "have to". there's a slight rhetorical difference ("would have to" carries the connotation that these forecasts are just hypothetical and don't actually have to be developed, or that at least it's not important, while "have to" implies that these forecasts are important and have to be made), but you don't have to make such rhetorical distinctions on the exam. in this case, you don't have to, since both choices involving "have to" (without "would") are wrong for other reasons. (a) is only wrong for the reason mentioned by the poster above me.
than 前后的对比要平行 前面用了have to know 后面than对比的也要do的形式 否则不平行 所以AE排除 economical是节省的 economic是经济的 所以应该选social and economic的选项 所以是D
specifically, the first verb is in a hypothetical/conditional tense (would have to know...), while the second verb is in the present tense (they do [= know] now). you are not allowed to imply such tense transitions. if you omit the verb, the omitted verb will be assumed to be in the same tense as its parallel counterpart. since you have to change tenses in this problem, you must include both verbs.
in A and E you are not comparing similar things demographers have to know a great deal more than now about social and economic ... literally you're comparing the knowledge about social and economic determinants to now. Consider the following example I have to run faster than now. This is clear incorrect. what is now? This doesn't make any sense I have to run faster than I do now. Correct
还是没懂，所以这个到底是什么的比较？又不是宾语A GREAT DEAL的比较，为什么要求now和a great deal要对等.....？现在对比较真的迷
0 0 回复 2019-01-15 12:26:09
成分相同才能省略 但前面是they would 后面是 they do 不相同 og有一道类似的 说的是地震还是电话来着 可以看看
0 0 回复 2019-12-09 23:59:06
more than 前后要平等
0 0 回复 2018-05-02 14:34:09
谁说的 别的题正确答案就是 主谓相同 主谓都可省略
0 0 回复 2019-01-15 11:31:37
would have to know是不很肯定的语气，其表达的是have to do的内容只是一个假设，并不是真的"必须"，而have to表达的意思是，要做的事情非常重要，"必须"去做。在本题中两种含义都合理，因此没有必要做这样的区分。