单项选择题：乳牙患龋特点为（）。 A.患龋率高，但范围不大 B.患龋率高，范围广泛 C.发病早，

题型：单项选择题

DNA ( Deoxyribonucleic acid ) is one of the most important discoveries in science. DNA is the plan for the human being , as a blueprint is the plan for building. DNA makes a person look the way he does. A person's DNA. comes from a mixing of his parents' DNA. That's why a child looks like his parents. But, besides controlling things such as height and hair color, DNA can also give people diseases , Scientists are now studying DNA to cure diseases.

In the seventies, scientists developed a process called recombinant (重新组合) or RDNA. Although it sounds difficult to understand, RDNA simply means taking DNA from one animal or plant and putting it into another. By doing so, scientists can create new beings. In so doing, scientists can better understand DNA, especially what parts of DNA do . After they understand DNA, scientists can begin to cure diseases. Often, the new being created will itself be the cure.

Besides curing diseases, RDNA research can also do other things. For example, scientists in Japan have already created “super-trees”. Trees help humans, because they take CO₂, which poisons humans, from the air and turns it into oxygen, which lets humans breathe. “Super-trees” do this too, but do if much faster. As things such as cars and factories have already put much CO₂ in the area, “super-trees” are badly needed.

Unfortunately, there is serious danger in RDNA research. Scientists want to create animals to cure old diseases, but these new animals may also create new diseases. It will be a serious problem if the animals escape from the science laboratory and into nature. As these animals are not natural, they may let loose many new powerful diseases.

As a result, RDNA research will create many solutions (解决方案), but it will also create many problems.

67. From the passage, we can know that a boy looks like his parents because________

A. he is son of his parents

B. his parents' DNA decides his appearance

C. he has received DNA from his father or his mother

D. scientists have put some of his parents' DNA into him

68. What does the underlined expression “let loose” probably mean?

A. let... go free B. get rid of C. absorb D. survive

69. What is the best title for the passage?

A. The DNA Research in Japan

B. A New Way of DNA Research in Japan

C. The Causes and Effects of DNA Research

D. The Advantages And Disadvantages of RDNA

70. The following statements are true about RDNA research EXCEPT_____.

A. the research has been stopped because the created animals carry virus

B. “super-trees” might be widely planted around the world

C. scientists have not completely understood DNA

D. RDNA research will benefit human beings a lot

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乳牙患龋特点为（）。 A.患龋率高，但范围不大 B.患龋率高，范围广泛 C.发病早，

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