To develop more accurate population forecasts, demographers have to know a great deal more than now about the social and economic determinants of fertility.
为了做出更准确的人口预测，人口统计学家必须比现在更多地了解生育率的社会和经济决定因素。
2
Competition is usually the more severe the denser the population.
通常是人口越密集，竞争越激烈
3
Rice is the staple food of more than half the world's population.