求助 GWD13套 第一套中的verbal第32题

GWD13套，第一套的V32:

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

给出的答案是E，我原来选的是D。难道 economical 不是节俭的意思吗？economic 表示经济因素的好像更加恰当。

谢过！不知道GWD里给出的标准答案正确率如何？