OG12-41

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

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d 选项中的“they do ” 为什么不能省略阿？是因为前后主语一致但是时态不一致吗？

I have more apple than you do.

You can't have "I have mroe apple than do."

"I" compare to "you"

You can't compare "They would have to know" with "Now"

去掉比较对象就变成了已知的知识和一个时间now比了

谢谢 !!  明白了 ~~