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题库 / Prep2008E2-SC-187
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)。
必须注意，would have to的出现在英语中有些限制，那就是要求本句或紧邻的上下文中如有“目前并非如此”之类的明确表达或与事实及公认常识明显不符，否则宜用have to而不是would have to。还有在强调“必须性”时，比如你说“法律规定，每个儿童都必须受教育”，尽管你知道有很多失学儿童，可这里是强调必须，就还得用have to而不能用would have to。
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