题目内容：

    We already know that exercise is good for our bodies. Daily exercise fights the loss of muscle tone and flexibility that tends to increase slowly with age. And it turns out that it has the same fountain-of-youth effects on our brains.

Studies show that over time our minds also become less flexible and nimble. We lose the ability to process new information or switch between mental tasks quickly — and now we know why.

A recent study examined nearly 100 individual studies on exercise and brain function and discovered exercising an average of 52 hours over six months is "associated with improved cognitive(认知的)performance in older adults with and without cognitive damage." The type of exercises that are beneficial include aerobic, strength-training and mind-body.

In previous studies, researchers from Japan's University of Tsukuba wanted to explore this idea by looking at the effect of exercise on this weakening of the brain. They tested the oxygen ability of 60 Japanese men between the ages of 64 and 75 who did not show any signs of dementia or other mental symptoms. Next, they looked at the brain activity of each man as he completed a mental task. They found that the fitter a participant was, the less brain activity he used to complete the tasks when compared with his out-of-shape peers(同龄人).

Although much research is focused on how exercise may benefit an aging brain, exercise offers brain health benefits at almost any age, and this includes children. A review of 14 studies showed that more physically active schoolchildren do better academically. Exercise actually causes your brain to grow in size. So get moving and keep moving for best results.

1.Which of the following best explains “nimble” underlined in Paragraph 2?

A.Intelligent. B.Dull. C.Unique. D.Simple.

2.What can we infer about the participants’ less-active peers?

A.They had significant brain advantages. B.Their brains were younger than their age.

C.They didn’t have to attend health classes. D.Their cognitive performance would decline.

3.How does the author support his idea?

A.By making comparisons. B.By analyzing study results.

C.By describing the processes. D.By telling his own experiences.

4.What’s the main idea of the text?

A.Exercise is beneficial for your bodies.

B.Exercise is especially good for the old.

C.Exercise can benefit your brain health.

D.Exercise may lower your risk of mental problems.