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Ever have one of those days when you just can’t focus on anything? If your brain just doesn’t feel as sharp as it should, water might be the answer. That advice comes from a new research effort that looked at the results of 33 different studies.
It’s already widely known that severe dehydration(缺水) causes all kinds of terrible things to happen with the human body, including both mental and physical side effects, but what’s particularly important about this new work is that it demonstrates that even a little dehydration can cause cognition problems.
In the summer months, when the sun is baking us and the heat is sending water out of our skin, mild dehydration can occur rapidly. A dehydration level of up to two percent can happen in just half an hour if you’re exercising or doing some kind of physical work in the summer heat, and that may be enough to cause your mental faculties to suffer.
This new study showed how dehydration could affect the human brain, and the results were striking. In one test designed as a card game, volunteers who were mildly dehydrated made 12 percent more errors than the control group who had enough water. Those same volunteers performed much better after their hydration levels were brought back up to normal.
No matter what kind of a job you do, making 12 percent more mistakes will be incredibly frustrating. If you feel like your brain isn’t running well, it might be time to down a bit of water, but exactly how much you need is still a topic of debate among medical professionals, as it can vary greatly from person to person.

1.What makes people less focused according to the passage?

A Lack of water.

B Being sharp enough.

C The important advice.

D A new research.

解析：选A。推理判断题。根据第一段第二句If your brain just doesn’t feel as sharp as it should, water might be the answer.可以推知是因为缺水才使得人们不能集中精力，故选A。

2.When will the cognition problems begin to happen from Paragraph 2?

A The moment when people have drunk enough water.

B The time when people suffer from mental side effects.

C The time when people just feel slightly thirsty.

D The moment when people have the severe dehydration.

解析：选C。细节理解题。根据第二段最后半句but what’s particularly important about this new work is that it demonstrates that even a little dehydration can cause cognition problems可知稍微缺水就会导致认知问题的发生，故选C。

3.How soon will the dehydration level reach 2% when exercising in the summer heat?

A In 30 minutes.

B Within 50 minutes.

C After 100 minutes.

D 150 minutes later.

解析：选A。细节理解题。根据第三段第二句的A dehydration level of up to two percent can happen in just half an hour if you’re exercising or doing some kind of physical work in the summer heat可知在炎热的夏季运动半个小时就会缺水，故选A。

4.What should people do when their brain isn’t running well?

A Have a debate.

B Drink some water.

C Wash the hands.

D Change the topic.

解析：选B。细节理解题。根据第五段第二句的If you feel like your brain isn’t running well, it might be time to down a bit of water可知当人们觉得脑子不好使的时候应该喝点水，故选B。