It all comes down to dopamine(多巴胺). Dopamine is a chemical in our body that send signals(信号) in the brain. It has many important roles: affecting memory, attention and how we learn. Our brains work best when there is a balance of dopamine - not too much or too little.

　　Our brains control dopamine in two ways. It either takes out dopamine quickly, or gradually, Exam success can be linked to how fast dopamine goes back to an even balance, according to new research from the University of Missouri, reported Yahoo.

　　What happens when we take an exam? If you become stressed, your brain will start to overload on dopamine. It is like a cup overflowing with water. The quicker you are able to go back to an even balance of dopamine, the quicker you can concentrate, helping you perform better on a test. Scientists found that, during a test, people who slowly got back to an even balance of dopamine scored 8 percent lower. That’ s the difference between a good mark and a bad mark.

　　But don’ t fear, there is good news for every students. The study also found that the more prACTice you get, the less stressed you’ ll be.

　　So, it turns out that prACTice really does make perfect.

　　46. Dopamine is a chemical in our body that ______.

　　A. puts us under a lot of pressure

　　B. sends signals in the brain

　　C. keeps our brains working

　　47. Which things does dopamine play a role in?

　　① remembering something

　　② having a good rest

　　③ paying attention to the teachers

　　④ choosing the way we learn

　　A. ①②③ B. ①③④ C. ②③④

　　48. What does the underlined word “ overload” mean in Chinese?