作者：文玉榮

A

Every living cell(細(xì)胞) contains genes(基因). They are too small to be seen in a microscope, but they are very important. Each set of genes in the body contains all the instructions needed to make a human being. Some genes determine hair color. Some determine the shape of a nose. Some genes help determine your height and even your weight.

Genes are made of a chemical called DNA-the letters stand for deoxyribonucleic acid(脫氧核糖核酸). In the early 1950's, two scientists, Francis Crick and James Watson, figured out how the parts of DNA fit together. Once scientists understood this structure, it became possible to take pieces of DNA apart and put them together in new ways. New kinds of genes could be made in this manner.

Scientists have studied the genes of many plants and animals. They have worked out which genes affect the color of a tomato and the thickness of its skin. Working out which genes determine which features is called genetic mapping, scientists have begun the Human Genome Project, an ambitious effort to map all the genes in the human body.

Some genes may be defective(有缺陷的). For example, something might be wrong with the gene that makes blood clot(凝聚). A baby born with this defective gene could suffer serious hemorrhages(出血) or even bleed to death because his or her blood fails to clot. If scientists ever learn how to map all the genes in our bodies, they can determine whether or not an unborn child has any defective genes. They might even discover how to treat these genes before the child is born.

1. What was the achievement of Francis Crick and James Watson?

A. They discovered why people have different hair colors.

B. They learned that some people bleed for long periods of time.

C. They looked at human cells under the microscope.

D. They worked out the structure of DNA.

2. What is the main idea of this passage?

A. Defective genes can never be repaired.

B. Genes are too small to be seen through a microscope.

C. Genes help scientists understand how living things develop their characteristics.

D. The Human Genome Project may explain the role of every gene in the body.

B

For more than twenty years scientists have been searching for signs of life on other planets. Most of these searches have been done over the radio. The hope is that someone in outer space may be trying to get in touch with us. Scientists have also sent radio and television messages on spaceships traveling through space, on the chance that someone may be receptive to such messages.

Scientists are using powerful radio telescopes to listen to signals from about 1,000 stars, all within 100 light years off Earth. In addition, they will scan(掃視) the entire sky to"listen" for radio messages from more distant stars. Using a computer, they will be able to monitor more than eight channels at one time. Scientists are looking for any signal that stands out from the background noise.

Of the 200 billion stars in the Milky Way Galaxy(銀河系), scientists find that five percent are like our sun. Perhaps half of them have a planet like Earth. Such a planet would be a reasonable distance from the star for temperatures to be right for the evolution(進(jìn)化) of life. Based on the inhabitable(可以居住的) planets in our galaxy, most scientists agree that chances are likely that one or more of these planets support some life.

However, many scientists wonder whether intelligent(有智力的) life exists on other planets. Some believe that twenty years of searching without any intelligible messages shows that no one is out there. They say that the evolution of intelligence comparable to ours is unlikely.

Other scientists believe that our search hasn't been long enough to rule out the possibility that intelligent life exists in our galaxy. Although our sun family is only about five billion years old, our galaxy is about 20 billion years old. In that time, some scientists think it is likely that civilization much more advanced than ours have developed. Perhaps these civilizations send us no signals;perhaps we have not recognized the signals they have sent us. If we hope to find intelligent life, these scientists believe that we have to keep looking.

3. How many planets in the Milky Way Galaxy might be inhabitable?

A. 5 billion. B. 10 billion.

C. 15 billion. D. 200 billion.

4. Which of these statements is true based on the information in the passage?

A. Our sun family is about 20 billion years old.

B. Most scientists believe that there is intelligent life on other planets.

C. Scientists try to send radio and television messages in order to get in touch with someone in outer space.

D. Scientists don't believe that there might be life on other planets.

[答案與解析]

1. D。第二段第二句即本題答案出處。2. C。第一段即說明了本文的主旨大意,基因有助于科學(xué)家們理解生物的特征是怎樣發(fā)展的。3. A。第三段第一句和第二句即本題答案出處。 4. C。根據(jù)短文最后一段第二句,可排除選項(xiàng)A;根據(jù)第四段第一句,可排除選項(xiàng)B;根據(jù)第三段最后一句,可排除選項(xiàng)D;第一段最后一句即本題答案出處。