求救！GWD最新13套的一道题

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.

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

 答案给的是E

可是WOULD 为什么要加

而且ECONOMICAL表示的是节俭的意思吗？

would是虚拟语气，我觉得答案应该是D,哪位大牛指点一下，为什么答案是E？

从意思上来看，必须要用虚拟语气，而economical坚决是“节俭”的意思，所以只能选d,大家请陈述意见。