A、The healthier twin is also the smarter one. B、The twins are as intelligent as each other. C、The raising environment has nothin

A new study proves the old Roman saying, "A sound mind in a sound body"—the more fit one’s heart is, the more one’s brain seems to benefit. The scientists discovered that cardiovascular fitness was linked with overall intelligence, although the same did not hold true for muscle strength and brainpower. Cardiovascular fitness was also linked with scores on tests of logical, verbal, technical and visual capabilities and even socioeconomic status and educational attainment later in life. Cardiovascular exercise increases blood flow to the brain, supplying it with more oxygen and nutrients. Moreover, during exercise, growth factors are produced that could improve brain structure over time. This not only includes more and stronger connections between nerve cells, but also more neurons and supporting cells. From animal experiments we know this is the case especially in the hippocampus, a region of the brain that is important for learning and memory. It is also possible that smarter people exercise more. However, the twin data suggests not. When the researchers looked at twins, they found that environment, not genetics, played the biggest role in these links. The fitter twin is also the more intelligent twin. Past research has suggested that cardiovascular fitness can benefit the minds of older adults. For instance, it can delay or reduce the onset and progression of dementia and Alzheimer’s disease. The findings can be used to argue for a more balanced school curriculum. It is a better argument for school kids to grasp that they can be more successful in life if they study and exercise.
16. What does the new study find?
17. How does cardiovascular exercise benefit our brain?
18. What do we learn about twins according to the researchers?
19. What enlightenment on education can be got from the research?