GWD1-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. D A. have to know a great deal than now about the social and economic B. have to know a great deal more than they do now about the social and economical C. would have to know a great deal more than they do now about the social and economical D. would have to know a great deal more than they do now about the social and economic E. would have to know a great deal more than now about the social and e D中 为什么是 than they do now 呢 不是应该是than they would now 吗多谢啦