It’s hard to say no to junk food. However, eating too much junk food can harm your brain, especially if you’re between the ages of 10 and 19.

“Junk food shapes teenagers’ brains in ways that are harmful to their ability to think, learn and remember. It can also make it harder to control impulsive（冲动的）behaviors,” said Amy Reichelt, a brain expert at Western University, Canada.

Reichelt and two other researchers reviewed more than 100 studies about how poor food choices can influence teen brains. They found teenagers are more sensitive（敏感的）to foods with a lot of fat and sugar, as their brains are not yet fully formed.

Teen brains are still developing the ability to control themselves. The prefrontal cortex（前额皮质）is the part of the brain that helps us do this. However, this part doesn’t fully develop until we are in our early 20s.

Besides, teen brains get more excited from junk food because it is regarded as a reward（奖励）. When we eat junk food, the parts of the brain will make us feel good, which are even more sensitive when we are young.

Reichelt and her team did their own study using mice, whose brains develop much like our own. They discovered that “teenage” mice that had a high-fat diet（饮食）performed worse on memory tests than those eating a normal diet.

So, what’s the best way to say no to junk food? Researchers suggest exercise. When we exercise, the brain’s reward system becomes less sensitive to food. Exercise also helps our brains grow and become better able to make smart decisions.

Do you ever wish you have more time? Everyone gets the same amount of time each day.     16     As a popular saying says, “Work smarter, not harder.”

The most important way to manage your time is to set priorities(优先权).     17     Also, consider whether or not they are urgent(紧要的) if they need to be done right away. It can be easy to forget important tasks that aren’t urgent, so make time for them.

Decide ahead of time what you’re going to do at certain times each day. Schedule time not only to meet people but also to do things alone. Then you can make sure everything gets done.

    18     Are you smarter in the morning, afternoon or evening? Schedule difficult tasks for times you feel good, and save easy ones for the times you’re tired.

Write down what you need to do and when. I keep two to-do lists: one for the present tasks and one for larger projects I’m working on.     19     And I don’t get discouraged by looking at a long list of items I can’t finish. I focus on the shorter list of each day’s tasks.

    20     When someone wants to give you a task, think carefully. Is it really important enough to spend your valuable time on? Could someone else do it instead?

In the end, using time well is about making a good plan and sticking to it.