GWD-1第32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economical，在这里面有什么含义？

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

我也正想问这道呢,还想问一下为什么than now about...对象不对称啊,怎么不用than they do now...呢?

答案好像是D吧？