Directions: There are three passages in this part. Each pas sage is followed by some questions or unfinished statements. For each of them there are four choices marked A, B, C and D. You should decide on the best choice and mark the corresponding letter on the Answer Sheet with a single line through the center. Passage 1 (76) Heredity(遗传) is not the only thing that influences our color. Where we live and how we live after we are born are important too. For instance, our genes influence how fat or thin we are. But our weight depends mainly upon how much we eat and how much exercise we get. In the same way, our skin color depends to a large extent upon how much sunshine we get. When summer arrives and light—colored people go to the beaches, some will tan darkly, some will tan lightly and few will not tan at all. Each one has inherited a different ability to tan, but the differences do not appear until the conditions are right. An outdoor man will soon become pale if he changes to an indoor job, while a desk clerk will take on tan after a short vacation in the sun. Sometimes people decide that being tanned is better than being pale. Sometimes they decide the opposite. Centuries ago, most of the people in Europe were peasants and they had to work in the fields all day. Noblemen, on the other hand, did not have to work. They stayed indoors and remained pale. You could always tell a nobleman from a peasant because a peasant had a tan. As a result, a shin so pale that the veins (血管) showed was considered a mark of great beauty. During the Industrial Revolution things changed. Farmers left their fields and went to work in factories, mines and mills. Working for long hours in dimly—lit factories and mines made their skins pale. (77) Wealthy people, however, could afford to travel so sunny countries. They had the leisure to lie around on the beaches and get tan. Having a tan became a sign of wealth. In Western Europe and North America pale skin is no longer desirable. Instead of bleaching themselves white with lemon juice, many women spend their time under a sun—lamp. The desire for a quick tan has led to the invention of pills and lotions (涂剂) that darken the skin artificially without exposure to sunlight. These pills and lotions can be bought by anyone at any drugstore. A rich man can spend hundreds of dollars on a vacation in the sunny West Indies and get his suntan there. But his lowest—paid clerk can have what looks like the same tan out of a bottle for a few cents. 1. Besides genes, our skin color has much to do with ______.