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If you go to a fast food restaurant．you will probably see a lot of teenagers． Today，many teenagers are overweight，and some of．this is because of their bad eating habits．， Most teenagers love food with a lot of fat，oil，salt，and sugar． People often call this kind of food "junk food"．

But． bad eating habits gobeyondfast food． We find many teenagers eat unhealthily． Some don't have breakfast before they go to school． During the day，some don't have a proper meal for lunch． In a recent survey at one school，scientists found that over two-thirds of the students didn't follow a healthy diet． They didn't like vegetables，and many of them didn't like to eat fruits． They preferred to eat food with a lot of salt，sugar，or fat．

Parents today also worry about their children's diet． Some doctors give the ．following ad-vice :

★Teenagers shouldn't eat too much junk food．

★ Teenagers shouldn’t eat food with too much salt． Salt can cause high blood pressure(高血压) in the future．

★Teenagers should eat food with less fat，oil，and sugar．

★Teenagers need to eat some fruits and vegetables every day: Fruits and vegetables arerich in vitamins(维生素 ) and have little fat．

★Teenagers need to drink more milk． Milk will help their bones grow．

★Teenagers need to eat breakfast every day． This is good for their body and mind．

(    )21．"Junk food" contains(包含) a lot of ________．