Nowadays, teenagers have changed considerably in comparison to the teens in the past. This is a "technology" generation. For teens in today's world, mobile phones, the Internet, and TV are essential parts of their everyday life. Most teenagers choose to watch TV and surf the Internet instead of reading books. They don't like reading because watching TV is easier and they don't have to use their own imagination. Teenagers prefer spending free time in front of a computer to doing physical activities such as playing football, riding bikes or going swimming. According to a recent study, teenagers growing up in the 1970s and 1980s enjoyed more than two hours of outside play each weekday, and a further nine hours at weekends, whatever the weather. However, today's teens play outside for just over an hour each weekday, and fewer than five hours on Saturdays and Sundays. Teens now often communicate with their friends by instant messages instead of talking face to face. When they want to share their feelings or some private thoughts, they will post them on Facebook. This makes it easier to get comments or receive encouragement from friends. Keeping a diary is unfashionable now. Teens now spend more time meeting friends in places like fast food restaurants or cafés. They like to eat fast food and sugary drinks more than home-cooked meals. This leads to obesity. Therefore, parents should encourage their children to play outdoors more. This helps them not only stay active and healthy but also socialize with friends as well as create treasured childhood memories.

The main purpose of this passage is to _________.