Facebook is an Internet-based social network site that lets people get in touch with family and friends and reach out to people with common interests around the world，all through computer．It is very popular，with more than 900million users．If Facebook were a country，it would have about three times the population of the United States．

Documents filed with US．financial regulators say Facebook has hundreds of millions of active users who send billions of messages each day and upload 250million photographs on their personal pages．Facebook users have registered 100billion"friends．"

On Facebook，"Friending"someone means you add the person to your list of people you can communicate with directly，which often allows the person to see more information about you than you share with the general public．

Facebook was started by Mark Zuckerberg and other students at Harvard University in 2004，and has grown at an amazingly fast pace．

Facebook makes money when advertisers pay to get access to hundreds of millions of Facebook users．Advertisers can often direct their messages to the people most interested in their products because Facebook computers keep track of information that users place on their pages．For example，a person interested in diving，planning a wedding，looking for work，or suffering from diabetes（糖尿病） may see advertisements related to those topics．

Facebook has become so much a part of the culture of the United States and other nations that it has been the subject of a Hollywood movie．It is a key marketing tool for many businesses，and its users'content has been used as evidence in some divorce or criminal cases．

29．From the first paragraph，we can learn that．___

A．about 900million Americans are using Facebook

B．Facebook is widely used in the world

C．Facebook is a country in the Internet

D．Facebook is a place where people can meet face to face

30．If you