.Fill in each numbered blank with one suitable word. In 2006, Facebook became available (1)_______________ anyone 13 years old and up. It caught on very quickly (2)_______________ over the world, especially among teenagers. Whenever they (3)____________ online, they took the time to post comments on their lives and to check messages (4)____________ friends. They also (5)_______________ photos and visited their friends’ Facebook pages in order to get updates. (6)______________, Facebook and similar social networking sites may be losing popularity among teens. Only 25% of teen in a 2013 study in the US kept in touch daily with others (7)_____________ these sites. And a small study in Australia, nearly one-third of teens questioned did not have (8)________________ on any social networking sites. Even Facebook owns 2014 business report containing (9)__________________ about less teen interest in the site. It looks like Facebook and other social networking sites have to (10)______________ a problem: how to keep teens interested!