问题, GWD13套题第一套题Q32

zijing4546

    

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

里面要考的语法点都不明白......
1, 啥时候用would have to know
2. 为什么可以用than now
3. economic 和economical有什么区别
请教大家结合这道题给我讲讲,谢谢!

shero

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

zijing4546

多谢~~~~~~~~~~~