To develop more accurate population forecasts, demographers have to know a great deal more than now about the social and economic determinants of fertility.
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 economical
我觉得would 表明的是一种虚拟假设,就是说,To develop more accurate population forecasts,那么demographers就应该怎么怎么样,所以用would have to 更好,但是我不明白为什么用economical 而不是economic, economic才能和social对应啊????