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) have to know a great deal more than now about the social and economic
(B) have to know a great deal more than they do now about the social and economical
(C) would have to know a great deal more than they do now about the social and economical
(D) would have to know a great deal more than they do now about the social and economic
(E)would have to know a great deal more than now about the socia/ and economic
题目分析：根据划线外的to develop的提示，我们知道划线开头应该以would开头更合适，A和B干掉。C开头说economical意思是节约的，意思不对，干掉。D和E一个加了they do一个没有加，如果加了就是将要知道的事情和现在知道的事情进行对比，如果不加就是将要知道的事情和现在（记住，没说“知道的事情”这个意思），显然是D的语义对比是合理的。
