中国是世界上人口最多的国家，印度紧随其后，但根据预测，印度未来将会超越中国，成为人口最多的国家。每个国家都会在一定的时间内进行人口普查，以便了解人口的基本情况，为公民制定更好的计划。

China has the largest population and India come after, but according to the prediction, India will pass China in the future and becomes the country with the largest population. Every country will do the census in the certain time, in the purpose of knowing the basic situation and making better plans for the citizens.
中国是世界上人口最多的国家，印度紧随其后，但根据预测，印度未来将会超越中国，成为人口最多的国家。每个国家都会在一定的时间内进行人口普查，以便了解人口的基本情况，为公民制定更好的计划。

Take America for example. It does the census every ten years. As it has many immigrants, so the population changes greatly in the last decade. The latest census showed that the white children became less and the Latin and Hispanic had the large birth rates, so it had been predicted that white children would become minority group in the future for America. As a result, the government has taken action to increase the local people to have children.
以美国为例。每十年做一次人口普查。由于移民很多，所以这里的人口在过去的十年里发生了巨大的变化。最新的人口普查显示，白人儿童越来越少，拉丁裔和西班牙裔人口出生率较高，因此有人预测，在未来的美国，白人儿童将成为少数民族。因此，政府采取行动，增加当地居民的生育率。

In China, thanks to the family plan, the large birth rate has been controlled and most people's life standard have been improved. Now the census predicts that China will face the aging time, so the government has changed the policy, inspiring people to have second child. The meaning of World Population Day is to remind the public of the importance of knowing the changes of the population. 
在中国，由于计划生育，人口出生率得到了控制，大多数人的生活水平得到了提高。现在人口普查预测中国将面临老龄化时代，所以政府改变了政策，鼓励人们生二胎。世界人口日的意义是提醒公众了解人口变化的重要性。