GMAT Sentence Correction (SC) | Re: To develop more accurate population forecasts, demographers

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

A. have to know a great deal more 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