(2015·山东省威海市二模)

Run, swim, lift weights, do yoga—do something, because it's good for you. Many studies tell us that regular exercise not only helps our bodies but improves memory, and eases anxiety. But what is happening to the mind during workout to create all these benefits?

A new study from Sweden suggests that a specific protein found in trained muscles might contribute to exercise's mental benefits. This protein, the researchers found, might help our bodies process molecules that, if out of balance, can stress us and contribute to depression(萎靡不振). The findings were published in the journal Cell.

To test this, the researchers kept attacking some mice with flashing lights, loud noises and interrupting their sleep for weeks. Predictably, this treatment makes the mice show signs and biochemical markers of depression.

But not all the mice showed those signs. One group, specially raised to have high levels of a protein called PGC­1alpha1 (the one in trained muscles), did not show those depression signs. PGC­1alpha1 increases production of an enzyme that breaks down a chemical called kynurenine. Kynurenine helps the body respond to an activated immune system(活性免疫系统), but it also plays a role in depression.

“Our original research assumption was that trained muscle would produce a substance(物质) with beneficial effects on the brain，” Jorge Ruas of the Karolinska Institute told Forbes.com. “We actually found the opposite: well­trained muscle produces an enzyme that removes harmful substances away from the body.”

This study was in mice, but it lines up nicely with all the other lines of evidence that exercise is good for mental health.

文章大意：体育锻炼有益身心健康，但是我们的大脑在锻炼过程中发生了什么变化从而有益于我们的身心的呢?本文给出了答案：锻炼的肌肉中产生了一种enzyme物质，它带走了我们身体里的有害物质。

12.According to the study, which of the following is bad for your mental health?

A.Protein. B.Molecule.

C.Enzyme. D.Kynurenine.

答案：D　细节理解题。由第四段最后一句话“...but it also plays a role in depression.”可知，Kynurenine会造成我们心情萎靡不振。该题易误选B项，由第二段倒数第二句话“molecules that, if out of balance, can stress us and contribute to depression(萎靡不振)”可知，该物质本身无害，只有当它在身体内失衡时才有害，所以不选。

13.What conclusion have the researchers drawn from the study?

A.Unbalanced exercise leads you to depression.

B.Well­fed mice survive better though being ill­treated.

C.Trained muscle produces a substance good for brain.

D.Regular exercise helps to clear rubbish away from body.

答案：D　细节理解题。由第五段最后一句话“...well­trained muscle produces an enzyme that removes harmful substances away from the body...”可知。

14.According to the last paragraph, the result of the study is ________.

A.reliable B.doubtful

C.predictable D.ambiguous

答案：A　推理判断题。该研究是在老鼠身上做的，但是它与其他研究非常吻合，所以该研究结果是可信的。

15.What's the main idea of the passage?

A.Why do you need regular exercise?

B.What matters most for your body?

C.How does exercise help your brain?

D.Why are mice chosen for the study?

答案：C　主旨大意题。由文章大意可知。