It's hard to imagine life before social media. If you asked a teenager what they would do if Facebook or Instagram suddenly disappeared, they might say that rneir life wouldn't be worth living. However, if we look at the history of social media, we can see that it is actually very new. The first social media site was called Six Degrees, and (18) _______ . It allowed users to create a profile and make friends with other users. The site was very popular, but it closed down in 2001. Other sites such as Friendster and MySpace appeared, but they were more about sharing music and photos than (19) _______ . Then, in 2004, Mark Zuckerberg created Facebook. At first, it was only available to (20) _______ but it quickly became very popular. In 2012, the company (21) _______ and its popularity increased even more. Today, there are over two billion monthly active users on Facebook. In 2005, YouTube was launched. (22) _______ grew very quickly, and in 2006, Google bought the site for $1.65 billion. Since then, various other social media sites have been created. Some of them are very popular, (23) _______

Mark the letter A, B, C, or D on your answer sheet to indicate the correct option that best fits each of the numbered blanks from 18 to 23.