To develop more accurate population forecasts, demographers have to know a great deal more than now about the social and economic determinants of fertility.
- have to know a great deal more than now about the social and economic
- have to know a great deal more than they do now about the social and economical
- would have to know a great deal more than they do now about the social and economical
- would have to know a great deal more than they do now about the social and economic
- would have to know a great deal more than now about the social and economic
答案D,我选的是E,为什么they do不能省略? |