2. 外语
  3. Defined biologically, hair is primarily composed of keratin, a protein, which grows out through the skin from follicles deep wit

Defined biologically, hair is primarily composed of keratin, a protein, which grows out through the skin from follicles deep wit

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问题 Defined biologically, hair is primarily composed of keratin, a protein, which grows out through the skin from follicles deep within the dermis. This definition holds for all mammals. What sets humans apart is not in the hair, but in the follicle. Under the microscope, an individual human’s hair follicles are anatomically indistinguishable, meaning that a hair follicle on your head is visually identical to one on your upper arm. Physiologically, however, the two follicles behave very differently. The first type, found in all mammals, produces terminal hair, the longer, darker, thicker hair generally found on the scalp, eyebrows, and eyelashes. The second type, particular to humans, produces the fine, unpigmented vellus hair found on most places of the human body, including the face and back. Vellus hair is usually very short and the follicles are not connected to sebaceous glands.
The main purpose of the passage is to
选项 A、introduce the idea that human hair is different from the hair of other mammals.
B、explain how terminal hair follicles change into vellus hair follicles.
C、describe the similarities between two types of human hair follicles.
D、compare the anatomy of human hair follicles with that of other types of hair follicles.
E、demonstrate that human hair growth contradicts the commonly held definition of biology.
答案A
解析 The best answer is A. The main purpose of this short passage is simply to introduce the idea that human hair is different from the hair of other mammals. Answer choices B, C, and D are too specific and beyond the scope of the passage. Answer choice E is not supported by information in the passage.
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