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Tham khảo đề thi - kiểm tra 'đề thi thử đại học khối a1, anh 2013 - phần 5 - đề 26', tài liệu phổ thông, ôn thi đh-cđ phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | PRACTICE TEST 30 Read the following passage and mark the letter A B C or D on your answer sheet to indicate the correct answer to each of the question The principle of use and disuse states that those parts of organisms bodies that are used grow larger. Those parts that are not tend to wither away. It is an observed fact that when you exercise particular muscles they grow. Those that are never used diminish. By examining a man s body we can tell which muscles he uses and which he does not. We may even be able to guess his profession or his recreation. Enthusiasts of the body building cult make use of the principle of use and disuse to build their bodies almost like a piece of sculpture into whatever unnatural shape is demanded by fashion in this peculiar minority culture. Muscles are not the only parts of the bodies that respond to use in this kind of way. Walk barefoot and you acquire harder skin on your soles. It is easy to tell a farmer from a bank teller by looking at their hands alone. The farmer s hands are horny hardened by long exposure to rough work. The teller s hands are relatively soft. The principle of use and disuse enables animals to become better at the job of surviving in their world progressively better during lifetime as a result of living in that world. Humans through direct exposure to sunlight or lack of it develop a skin color which equips them better to survive in the particular local conditions. Too much sunlight is dangerous. Enthusiastic sunbathers with very fair skin are susceptible to skin cancer. Too little sunlight on the other hand leads to vitamin-D deficiency and rickets. The brown pigment melanin which is synthesized under the influence of sunlight makes a screen to protect the underlying tissues from the harmful effects of further sunlight. If suntanned person moves to a less sunny climate the melanin disappears and the body is able to benefit from what little sun there is. This can be represented as an instance of the principle
