阅读下面短文,从短文后的选项中选出可以填入空白处的最佳选项。选项中有两项为多余选项。
A healthy person is a wealthy person. Wealth is here valued in terms of the person's physical well-being, which means he or she is able to get about and carry out day-to-day tasks easily. 16 () To achieve this, physical exercise is a must.
17 () Modern-day diseases like heart problems, diabetes(糖尿病), and certain cancers are often caused by a lack of exercise. People with these diseases can feel better if they include exercise in their daily lives. Regular exercise also improves sleep quality, which in turn helps protect us from these diseases.
18 () During space missions, their bones, internal organs, and cardiovascular (心血管的) system are all affected by low gravity. However, it has been found that exercise can significantly reduce these negative changes.
Exercise makes us lose weight too. It burns the energy. In our push-button lifestyle, we have become quite sedentary(惯于久坐不动的). "Why walk, when we can take the car" seems to be the way of life for many of us. 19()Moreover, we seem to be only "exercising" our fingers as we play computer games, surf the Net, and press the keys to choose our favorite television programs.
Lastly, students should exercise at least three times a week for at least twenty minutes each time, as exercise is a good stress killer. 20() Some of them can help a person feel less stressed and more cheerful. Students will perform better in their studies.
In short, regular exercise helps us not only feel younger but also look younger.
A. Exercise is key to good health.
B. Exercise is also important for astronauts.
C. He or she will look good and feel good.
D. Students are busy with heavy homework.
E. Nowadays, even shopping is done online.
F. It is no wonder that we are gaining weight.
G. Exercise causes the brain to produce different chemicals.

16. C 根据上文“Wealth is here valued in terms of the person's physical well-being, which means he or she is able to get about and carry out day-to-day tasks easily.”可知，健康的人能够四处走动并轻松地进行日常工作，这与C项(他或她会看起来身体和精神都很好。)表达的含义一致，故选C。
17. A 根据下文“People with these diseases can feel better if they include exercise in their daily lives”可知，锻炼能改善病人的健康状况，这与A项(锻炼对健康很重要。)表达的含义一致，故选A。
18. B 下文“During space missions, their ... reduce these negative changes.”提到执行太空任务的人通过锻炼可以减轻工作对身体的负面影响，是对段首句的具体说明。B项(锻炼对宇航员也很重要。)承上启下，符合语境，故选B。
19. F 空前两句说的是在当代按键式的生活方式中，我们变得久坐不动，F项(难怪我们的体重在增加。)是上文的结果，且gaining weight对应段首句中的lose weight这一锻炼的好处。故选F。
20. G 根据下文“Some of them can help a person feel less stressed and more cheerful.”可知，空处提到一些与缓解压力和调动情绪相关的事物，G项(运动使大脑产生不同的化学物质。)符合语境，下文的them指代选项中的different chemicals。故选G。