Directions: There are 2 passages in this section. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked （A）, （B）, （C） and （D）. You should decide on the best choice and mark the corresponding letter on Answer Sheet 2 with a single line through the centre.
Questions 57 to 61 are based on the following passage.
In an experiment published last month, researchers from the University of Illinois recruited schoolchildren, ages 9 and 10 and asked them to run on a treadmill, hoping to learn more about how fitness affects the immature human brain.
The researchers sorted the children, based on their treadmill runs, into highest-, lowest- and median-fit categories. Only the most- and least-fit groups continued in the study （to provide the greatest contrast）. Both groups completed a series of cognitive （认知的） challenges. Finally, the children's brains were scanned, using MRI technology to measure the volume of specific areas.
Previous studies found that fitter kids generally scored better on such tests. And in this case, too, those children performed better on the tests. But the MRIs provided a clearer picture of how it might work. They showed that fit children had significantly larger basal ganglia, a key part of the brain that aids in maintaining attention and "executive control". Since both groups of children had similar socioeconomic backgrounds, body mass index and other variables, the researchers concluded that being fit had enlarged that portion of their brains.
The findings arrive at an important time. For budgetary and administrative reasons, schoolboards are reducing physical education, while on their own, children grow increasingly sluggish （懒散的）. Roughly a quarter of children participate in zero physical activity outside of school.
At the same time, evidence accumulates about the positive impact of even small amounts of aerobic （有氧的） activity. Past studies found that "just 20 minutes of walking" before a test raised children's scores, even if the children were otherwise unfit or overweight.
But it's the neurological （神经的） impact of sustained aerobic fitness in young people that is especially compelling. A years-long Swedish study published last year found that, among more than a million 18-year-old boys who joined the army, better fitness was correlated with higher IQs, even among identical twins. The fittest of them were also more likely to go on to profitable careers than the least fit, rendering them less likely to live in their parents' basements.
No correlation was found between muscular strength and IQ scores. There's no evidence that exercise leads to a higher IQ, but the researchers suspect that aerobic exercise, not strength training, produces specific growth factors and proteins that stimulate the brain.