问题补充：
Have you ever wondered why there are so many skin colors in the world? Do you know why people living in particular areas usually have a certain color? Biology and history are the two reasons for this.
Skin contains something called melanin, which determines a person’s skin color. The more melanin a person has, the darker his or her skin will be. The amount of and the production of melanin are controlled by genetics, but can be affected by other things, such as sunlight. If a person lives in a place with less sunlight, a person’s body will produce less melanin, making the skin lighter.
Skin color is also affected by another source ---- vitamin D. humans all need vitamin D to build bones. People can get it by eating foods such as fish and milk, or from sunlight, so sunlight absorbed by melanin cannot be used for vitamin D production. Therefore, a dark—skinned person will produce less vitamin D than a light—skinned person when they received the same amount of sunlight.
The connection between vitamin D production and skin color is clear when we look at evolution. The earliest humans lived in Africa, their dark skin produced less vitamin D because of their dark skin. As a result, their skin made less melanin, so they could get enough sunlight to produce vitamin D. their skin gradually got lighter and they lost hair. Now, people living in areas with strong sunlight like Africa, have darker skin, while people living in other areas have lighter skin. The exception to this is the Inuit, who live in a place with little sunlight, but have dark skin because they eat a lot of fish and have enough vitamin D.
Evolution has given us a rainbow of skin colors. Humans have always had melanin to determine our skin color. What has changed through history is the environment where we have lived. This has in turn changed our melanin production, and eventually, skin color.
Brief _【小题1】
People living in a particular 【小题2】 usually have the same skin color and there are
many different skin colors in the world.
Reason for skin color
The reasons for different skin colors mainly【小题3】 in biology and history.
Biology reasons
The amount of melanin, by which a person’s skin color is【小题4】 , varies from people to people. The more melanin a person has, the 【小题5】 his or her skin will be.
Vitamin D is another source【小题6】 skin color. Vitamin D is necessary for humans to
build bones Sunlight contributes to vitamin D in the skin.
Historical
reasons
The earliest people in Africa had dark skin with hair covering it because the sunlight is very strong.
When they moved to places where they could not get enough sunlight to【小题7】
vitamin D, their skin color became lighter.
Generally speaking, people in areas with strong sunlight, have darker skin 【小题8】 people in other areas have lighter skin.
【小题9】
Melanin_【小题10】an important role in our skin color. With our living environment changing, melanin production is changed, which leads to the changes in our skin color.
Introduction
答案：
(答案→)Introduction
解析：
【小题1】Introduction归纳总结题。归纳全文是关于为什么会有各种不同的肤色的原因。
【小题2】area原词再现。根据第一段第2行in particular areas。
【小题3】lie同义句转换。根据第一段最后一句Biology and history are the two reasons for this.说明肤色不同是因为生物学和遗传，故转换成原因在于lie in
【小题4】determined句式转换。根据第二段第一行which determines a person’s skin color，把这个主动句变成了被动形式。
【小题5】darker原词再现。根据第二段1,2行The more melanin a person has, the darker his or her skin will be.
【小题6】affecting同义句转换。根据第三段第一句Skin color is also affected by another source ---- vitamin D.转换成现在分词短语修饰another source。
【小题7】produce原词再现。根据第四段第四行they could get enough sunlight to produce vitamin D. their skin gradually got lighter and they lost hair.
【小题8】while原词再现。根据第四段Now, people living in areas with strong sunlight like Africa, have darker skin, while people living in other areas have lighter skin.
【小题9】conclusion归纳总结。Conclusions就是上文得到的最后的结论。
【小题10】plays 固定词组。Play a part/role in…主语是不可数名词Melanin，故用单数形式。
