Do you know what a census is? 你知道什么是人口调查吗？

　　It is an official survey of a country to learn about people living in the country. 它是一个国家用来了解人民生活的官方调查。

　　In the United States, there is a government agency that takes the census. 在美国，有一个政府机构负责人口调查。

　　It sends survey letters to every household in the United States. 它向美国的每个家庭发送调查信件。

　　The survey asks the number of people in a household, their age, gender, jobs and so on. 调查询问家庭人数，他们的年龄、性别和工作等等。

　　In ancient Rome, a census was taken to record the number of adult men for military service. 在古罗马，人口调查用于记录参军的成年男子人数。

　　But now, countries take censuses to learn about their citizens and plan various policies. 但现在，国家实施人口调查用来了解公民和计划各种政策。