To develop more accurate population forecasts, demographers have to know a great deal more than now about the social and economic determinants of fertility.
In the correct answer D, why use "should have to" instead of using " have to"?
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