America's Census Bureau simply assumes that currentfertility rates will persist.
美国人口普查局作出简单假设，目前的生育率将持续一段时间。
2
The target reductions in fertility rates were reached long ago. Current rates, he says, are below replacement levels and are unsustainable.
他说，生育率的下降目标早已实现，现在的生育率已经低于人口替换率，这会导致失衡。
3
Stabilization of the world population at 8 billion or below by 2050, through a voluntary reduction of fertility rates, rather than the current trajectory of more than 9 billion by midcentury