问题 单项选择题

DNA复制不需要的酶是______

A.DNA聚合酶

B.解螺旋酶

C.DNA连接酶

D.DNA拓扑异构酶

E.限制性核酸内切酶

答案

参考答案:E

解析:DNA复制需要DNA聚合酶、解螺旋酶、DNA拓扑异构酶、DNA连接酶等,限制性核酸内切酶是在重组DNA技术中常用的工具酶,它能识别DNA的特异序列,并在识别位点或其周围切割双链DNA,以便进行目的基因和载体的连接。

阅读理解

In 1955, a man named Raymond Kroc entered a partnership with two brothers named Mcdonald. They operated a popular restaurant in California which sold food that was easy to prepare and serve quickly. Hamburgers, French fries, and cold drinks were the main foods on the limited menu. Kroc opened similar eating places under the same name, “McDonald’s” and they were a quick success. He later took over the company and today it is one of the most famous and successful “fast-food” chains(连锁店) in America and the world.

Why was his idea so successful? Probably the most important reason was that his timing was right. In the 1950s, most married women stayed home to keep house and take care of their children. During the 1960s, the movement for equality(平等) between men and women and an economy(经济) that needed more families to have two money-earners resulted in many women returning to the workplace. This meant that they had less time and energy to do housework, so they depended more on fast-food restaurants.

Single parents also have little time to spend in the kitchen. People living alone because of divorce(离婚) or a preference for a “single lifestyle” also depend on this type of food, since cooking for one is often more trouble than it is worth.

Fast food is not part of the diet of all Americans. Another of the 1960s was called back-to-nature movement. More and more Americans based their diets on natural foods. This preference for natural foods continues to this day. These products can now be found not only in the special health food store but also in many supermarkets.

小题1:The passage is mainly about ____.

A.how and why “McDonald’s” became successful

B.the effect social and economic changes have on people’s eating habits

C.why Americans prefer natural food

D.American eating habits小题2:Which of the following was NOT a reason for Raymond Kroc’s success?

A.His partnership with the McDonald brothers.

B.A changing economy.

C.The back-to-nature movement.

D.Women’s equality movement.小题3:We can infer from the passage that ____.

A.natural foods can also be found in McDonald’s

B.many married women in America returned to work in the 1960s

C.McDonald’s fast food is popular among the young

D.divorce caused people to change their eating habits

单项选择题