根据短文理解选择正确答案。

       The one-child policy in our country has made most families much smaller than before. That is to say, there are fewer children in a family. But the population of China is still growing faster. Why? In fact, it's a serious problem not only in China, but also in the whole world. It's reported that the world population isexpectedto reach 10,500,000,000 by 2050.There are two important reasons. First, there are still more and more babies born every year. Next, people in the world can live much longer than before.

      The earth is too tired, but it has to burden(担负)more in the future. Who can save her?