问题, GWD13套题第一套题Q32

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

选d

1 一般现在时变过去将来时是表示建议的虚拟语气

2 用than they do now； than now很少可能会对

3 ecomonic经济的 经济学的 economical节约的