It's hard to refuse hamburgers，French fries，potato chips.And all of the other junk food that seemed to call out to us.However，eating too much junk food can harm your body，particularly if you are between the ages of 10 and 19.
    "Junk food shapes teenagers'（青少年） brains in ways that impair their ability to think，learn and remember.It can also make it harder to control impulsive（沖動的） behaviors，" said Amy Reichelt.A brain and nutrition specialist at Western University，Canada."It may even up a teen's risk of unhappiness and anxiety."
    Reichelt and two other researchers reviewed more than 100 studies about how poor food choices can influence（影響） teenagers' brains.They found teenagers are more sensitive（敏感的） than any other age group to man-made foods with a lot of fat and sugar and their brains are not yet fully formed.
    Teenagers' brains are still developing the ability to assess（評估） risks and control actions.The prefrontal cortex（前額皮質）is a part of brain.It tells us we should not eat chips all the time and helps us resist the urge.However，this region is the last to mature-it doesn't fully develop until we are in our early 20s.
    Meanwhile，teen brains get more excited from rewards.The parts of the brain that make us feel good when we do something pleasurable-like eating tasty foods-are fully developed by the teens year.
    In fact，these regions are even more sensitive when we are young.That is because dopamine（多巴胺），a natural chemical that lifts our mood when we experience something good，is especially active in teen brains.
    Therefore，the teen brain has two actions against it when it comes to resisting junk food."It has a stronger drive for rewards and less self-regulation（自我調節），"said Reichelt.
    So what's the best way to say no to junk foods？Researchers suggest exercise.When we exercise，the brain's reward system（系統） becomes less sensitive to food clues.Exercise also pushes the body to make a protein（蛋白質）.It helps brain cells grow and form connections between the prefrontal cortex and other brain regions.The prefrontal cortex thus can work better to help us make wise decisions and control our impulses.

（1）The word "impair" in paragraph 2 probably means

B

B

.
A.improve
B.weaken
C.change
D.influence
（2）According to the passage，teenagers are more sensitive to

C

C

.
A.Milk
B.Salad
C.Ice-cream
D.Strawberries
（3）What is the writer's main purpose in writing the last paragraph？

C

C

A.To discuss why teenagers prefer the junk food.
B.To stress that it is difficult for teens to resist the junk food.
C.To suggest that teens do more exercise to resist the junk food.
D.To question whether our mood could suffer from eating junk food.
（4）What can we learn from the passage？

A

A

A.Dopamine can lift our mood when we exercise.
B.Fat and sugar in the junk food is bad for our health.
C.The prefrontal cortex is fully developed by the teen years.
D.Having more junk food may cause unhappiness in teens.