prep2-187

187.
            (32525-!-item-!-188;#058&007080)     (GWD-1-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.

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 social and economic

请问A为什么不对？不是说情态动词不能随便加吗？而且than they do now 得they do 可以省略吗？

谢谢

及物动词接宾语的时候 比较要求补全 不然有歧义

比如 i ate more food than you did. 如果不加可以被理解为我吃食物比吃你多

我怎么觉得这句活know后面没有宾语呢？

请教啊

首先时态来讲应该用虚拟语气，因此是would have to.

其次they do我觉得是可以省略的，就跟你说的这个结构是主谓缺少宾语的结构，I eat more than you(do可以省略)，又因为前后主语相同所以they也可以省略。