TTGWD 14-Q32

GWD 14套：

verbal 部分

Q32:

To develop more accurate population forecasts , demographers have to know a great deal more than now about social and economic determinants of fertility.

A. have to know a great deal more than they do now about the social and economic

D. would have to know a great deal more than they do now about the social and economic

答案是D，我选A

请问这里又没有虚拟条件，To develop…只是表目的，为什么要用虚拟would have to而不是have to?

好像没有人问过这题，谢谢哪位知道的话给点意见吧