(2015·山東省威海市二模)

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(活性免疫系統(tǒng)), but it also plays a role in depression.

“Our original research assumption was that trained muscle would produce a substance(物質(zhì)) 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：體育鍛煉有益身心健康，但是我們的大腦在鍛煉過程中發(fā)生了什么變化從而有益于我們的身心的呢?本文給出了答案：鍛煉的肌肉中產(chǎn)生了一種enzyme物質(zhì)，它帶走了我們身體里的有害物質(zhì)。

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　細節(jié)理解題。由第四段最后一句話“...but it also plays a role in depression.”可知，Kynurenine會造成我們心情萎靡不振。該題易誤選B項，由第二段倒數(shù)第二句話“molecules that, if out of balance, can stress us and contribute to depression(萎靡不振)”可知，該物質(zhì)本身無害，只有當它在身體內(nèi)失衡時才有害，所以不選。

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　細節(jié)理解題。由第五段最后一句話“...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　推理判斷題。該研究是在老鼠身上做的，但是它與其他研究非常吻合，所以該研究結(jié)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　主旨大意題。由文章大意可知。