大全一题

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

1. have to know a great deal more than now about the social and economic
2. have to know a great deal more than they do now about the social and economical
3. would have to know a great deal more than they do now about the social and economical
4. would have to know a great deal more than they do now about the social and economic
5. would have to know a great deal more than now about the social and economical

为什么用would 啊？．．．还有为什么是答案e?

请指点，谢谢

答案是d吧

就是考两点，一个是比较内容的前后一致

另一个是economic和economical的区别，

感觉e不对