Performing better under pressure

What is the most stressful thing in school? It is probably exams．．       But some students succeed under pressure，while others struggle．So，why do some students perform better under stress?
It all comes down to dopamine （多巴胺）． Dopamine is a chemical in our body that sends signals （信号） in the brain．It has many important roles：affecting memory，attention and how we learn．．       
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 a balance，according to new research from the University of Missouri，reported Yahoo．
．       If you become stressed，your brain will start to overload （起负荷） on dopamine．It is like a cup overflowing with water．The quicker you are able to go back to a balance of dopamine，the quicker you can concentrate．．      
Researchers found that，during a test，people who slowly got back to a balance of dopamine scored 8 percent lower． That’s me difference between a good mark and a bad mark．
But don't fear，there is good news for every student．．    So，it turns out that practice really makes perfect．
根据短文内容，从下面五个选项中选出能填入文中空缺处的最佳选项，使短文意思通顺、内容完整，并在答题卡上将该项涂黑。

A．This will help you perform better on a test．

B．Exams can put us under a lot of pressure．

C．The study also found that the more practice you get，the less stressed you’ll be．

D．What happens when we take an exam?

E．Our brains work best when there is a balance of dopamine—not too much or too little．