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1、Unit 3 Language in use 习题1. 任务型读写Have you ever wondered why there are somany skin colours in the world? Do you knowwhy people living in particular areas usually have a certain colour? Biology and history are thetwo reasons for this.Skin contains some thing called melanin, which determines a person s
2、 skin colour. The moremelanin a person has, the darker his or her skin will be. The amount of and 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 strong sunlight, his or her skin will protect itself by produci
3、ng more melanin, makingthe skin darker. In a place with less sunlight, a person the skin lighter. s body will produce less melanin, makingSkin colour 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 fr
4、om sunlight, which causes vitamin production in the skin. Melanin protects skin by absorbing sunlight, so sunlightabsorbed 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 o
5、f sunlight.Evolutionhas given us a rainbow of skin colours. Humans have always had melanin todetermine our skin colour. What has changed through history is the environment where we have lived. This has in turn changed our melanin production, and eventually, skin colour.People living in a particular
6、(2)usually have the same skinBrief (1)colour and there are many different skin colours in the world.Reasons forskinThe reasons for different skin colours mainly (3)in biologycolourand history.The amount of melanin, by which a per son s skin colour isBiological(4), varies from people to people. The m
7、ore melanin a personreasonshas, the (5)his or her skin will be.VitaminD is another source (6)skin colour. VitaminD isHistoricalnecessary for humans to build bones. Sunlight contributes to vitamin Dproduction in the skin.The earliest people in Africahad dark skin with hair covering itbecause the sunl
8、ight is very strong.When they moved to places where they could not get enoughreasonssunlight to (7)vitamin D, their sk in colour became lighter.Generallyspeaking, people inareas withstrong sunlight,havedarker skin(8)people in other areas have lighter skin.Melanin (1 0)an important role in our skin c
9、olour. With our(9) living environment changing, melanin production is changed, which leads to the changes in our skin colour.2. 单项选择1. Where is Mike? He has gone away _ the weekend.2. _ a boy, he used to help his father on the farm.3. _ no need for us to discuss the problem again since it has been settled.4. His failure made his father think him a _ boy.5. This is the best way I can think of _ the problem.6. The days we look forward to _ at last.A. comingB. cameC. comesD.be coming