[简答题]

Despite wars, famines, and epidemics, Earth’s population is booming ahead to new records—with no end in sight.
Every day, the world adds enough people to populate a medium-sized city in the US. In one month, the number of new-world citizens equals the population of New York City.
Every year, there are 90 million more mouths to feed, more than the total population of Germany.
Several factors are propelling this rapid growth, including an element that is often overlooked: the huge number of teenagers who are becoming mothers, particularly in the countries of sub-Saharan Africa.
In four African nations—Niger, Mali, Sierra Leone, and Ivory Coast—1 out of every 5 adolescent females of childbearing age has a baby annually.
The US Bureau of the Census says this high rate of motherhood among teens has helped to maintain the high pace of births across most of the African continent. By starting a family early, a typical woman in Som