economical还是economic?

GWD1-Q32:

To develop more accurate population forecasts, demographers have to know a great deal more than now about the social and economic determinants of fertility.

1. have to know a great deal more than now about the social and economic
2. have to know a great deal more than they do now about the social and economical
3. would have to know a great deal more than they do now about the social and economical
4. would have to know a great deal more than they do now about the social and economic
5. would have to know a great deal more than now about the social and economical

答案是E,但是我觉得A在逻辑意思表达上可能会更好。

理由1：第一个分句是To引导的目的状语，表明 demographers为了达到这个目的，不得不了解（have to learn）更多的determinants of fertility，而E则是would have to，虚拟语气。

理由2：social 和 economic 在意思上并列一致，“人口出生率在社会上的和经济上的决定性因素”，而E是economical，更强调“经济上节约的”，“节约的决定因素”逻辑意思不符。

不知道我这么理解有没有问题，还请大家帮助解答、指教：-）谢谢

E是肯定有问题的

http://forum.chasedream.com/dispbbs.asp?boardid=23&replyid=565327&id=59335&page=1&skin=0&Star=7

这题貌似还没确定下来

这题是OG12的第41题

OG的解释

this sentence explains a hypothetical situation and therefore calls for a conditional-or contrary-to-fact-construction, because in order to more accurately predict population, demographers would have to know more than they presently know.A present-tense verb is required to describe the current state of demograhpers' knowledge, and the comparison made by the sentence must be between current and conditional knowledge, not between knowledge and time of knowing(now).

A.wrong comparison-between knowledge and time(now);conditional verb is needed

D.conditional knowledge, indicated by would have to know, is correctly compared to current knowledge.

这题在OG12上答案是D

A than的比较对象不对等

economic和economicial含义不一样，不能互换

而且D加了would更准确了

大家看参考书还是要小心，一个印刷错误会导致你浪费半小时。