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题库 / OG2015-SC-42
To develop more accurate population forecasts, demographers have to know a great deal more than now about the social and economic determinants of fertility.
have to know a great deal more than now about the social and economic
have to know a great deal more than they do now about the social and economical
would have to know a great deal more than they do now about the social and economical
would have to know a great deal more than they do now about the social and economic
would have to know a great deal more than now about the social and economic
题目分析：
本题具有比较词more…than…。
选项分析：
A选项：比较对象不正确，我们应该比较的是不同时间的两件事，而不是两个时间（now）。
B选项：economic和economical的意思不同，前者是“经济”的意思，后者是“节约的”意思，在逻辑上，和“社会(social)”产生并列关系的应该是“经济”，而不是“节约的”。
C选项：economic和economical错误同(B)。
D选项：Correct. 本选项在语法和逻辑上均是正确的。
E选项：比较对象不正确错误同(A)。
know a great deal in the future than now
否则的话就可以理解为比较对象不一致
如果要省略they know 前面也要有同样的they know， 而前面的成分是have to know 补到后面意思不对
1）比较错误
D：would 【have to know】 a great deal more than 【they do now】 about the social and economic，比较对象为【不同时间下的两件事】✔
E：would 【have to know】 a great deal more than 【now】 about the social and economic，比较对象为时间❌
由于前句没有时间状语，后句只能被理解成为【now】，而并不能理解为【省略了谓语动词】
than 前后应有相同成分，就这题而言，前面应有时间状语，后面才能直接跟now
know a great deal in the future than now
否则的话就可以理解为比较对象不一致
如果要省略they know 前面也要有同样的they know， 而前面的成分是have to know 补到后面意思不对
2.比较More than，后面直接接now是不对的，比较对象不明确，
只有在more than前面也有时间状语的时候，可以直接接now,省略前面的主句
AE错。
题干想表达的意思是他们必须比现在知道的更多，但是如果省略they do意思就变成了必须比不得不知道的知道的更多，不合理，排除AE
A，省略后变成they have to know now，错误，是现在已知的，不是现在不得不知的；would在这里是表示可能性的虚拟语气，保留能更好地表意
+1
would可以表示意愿及可能。
eg.:
Right: I have never seen an aardvark, but my father has.
Wrong: I have never seen an aardvark, but last year my father have.
Right: I have never seen an aardvark, but last year my father saw one.
除非不会导致歧义，如：
Our cars were designed to inspire envy, and they do.
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
have to是情态动词，表语气不得不，但不同于must/can等情态动词，have to有人称和时态变化，否定式是don't have to，其省略式用助动词do；
have/has done里，have是助动词，表时态，其省略式直接用have/has，不用助动词do，sb have done sth as other people has
Eg:
Scientists have gathered evidence suggesting that complex life-forms emerged much earlier than previously thought.
than previously thought (when they emerged)
时间状语的比较，能否省略取决于than前面是否有相应的时间状语。有则than后面主句可以省略；没有则than后面需要补出主谓，以避免比较对象上的歧义。
Eg:
Right: Prices are only 1.3 percent higher this year than last year.
Wrong: Prices are only 1.3 percent higher this year than last year's.
economical 节约的 节约的 经济适用的
economic 经济的 经济的 经济的 牛逼经济的