2021年成人英语三级考试阅读理解练习题（五）

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DNA

Each living cell contained the message EAT, GROW, SPLIT, AND PASS THIS MESSAGE ALONG. But how could cells understand a message> they couldn’t read or write, so what form could these instructions take? For a long time this question baffled (使困惑)scientists, and they worked hard to figure out how the messages of life were passed from generation to generation.

Then in 1953, four scientists solved the mystery. James Waston and Francis Crick, helped by the work of Maurice Wilkins and Rosalind Franklin, figured out the structure if a super-molecule(超分子)called DNA (short for deoxyribonucleic acid 脱氧核糖核酸的缩略)，which contains the cell messages. The three men became world famous and won the Nobel Prize, which is one of the highest honors a scientist can be awarded. But Rosalind Franklin died before people realized how important her work was.

Because DNA is too small to be seen under a microscope, the scientists had to figure out how the molecules that made DNA were fitted together. They discovered that the DNA molecule looked like a twisted rope ladder (扭曲的绳梯), which they called a double helix(双螺旋). The “rope” and “steps” of the DNA, they said, were made of four kinds of nucleotide (核甘)bases hooked together in special ways that could carry the coed messages of life.

DNA is in the middle of all living cells. It acts as a memory and control for all growth and reproduction. Each “step” in the twisted ladder is a coded “word” of instructions telling the cell how to build itself up step by step, and when to split in two.

When a cell divides, the DNA “unzip”(解开拉练) into two strands (串)，one for each new cells. Each DNA strand contains the full message, and immediately starts building itself back to a double helix by using the chemicals “eaten” by the cells. Soon each cell in the new generation has a full DNA molecule inside it, just like the one in its parent cell. Then the process of growth and division starts all over again.

1. Which of the following statements is not true?

A. Each living cell can take instructions. B. The DNA molecule is a twisted rope ladder.

C. DNA acts as a memory and control center for all growth and reproduction.

D. DNA gave the first living cells the ability to split and started the amazing story of life.

2. It can be inferred from the passage that ______.

A. Rosalind Franklin won the Nobel Prize for her work on DNA

B. People did not solve the mystery of DNA until the year 1853

C. The discovery of DNA has exerted a profound influence on scientific world

D. Maurice Wilkins died before people realized how important his work was

3. According to the passage, the DNA molecule turns out to be ____.

A. a twisted rope ladder B. “steps” C. coded “words” D. four kinds of nucleotide bases

4. The phrase “the coded messages of life” in the third paragraph can be best replaced by _____.

A. the instructions to eat, grow, split and to pass this message along

B. the process of cell growth and cell division C. the instructions to build itself up

D. the instructions to split itself in two

5. In the final analysis, a double helix signifies____.

A. the chemicals “eaten” by the cell B. the structure of a super-molecule called deoxyribonucleic acid

C. the two strands, one for each new cell D. the parent cell and the body cells

内容提示与分析： 本文主要围绕DNA讲述了一些生物技术的知识。文章开头提出的问题是：为什么生命信息从一代传向下一代?科学家发现DNA正是秘密所在。随后介绍了DNA的双螺旋结构。DNA处于活细胞的中心，象个记忆库记忆着信息;最后介绍了DNA通过自我复制生成新的DNA的过程。

答案及分析：1. B分析：文章第三段第二句提到：“They discovered that the DNA molecule looked like a twisted rope ladder, which they called a double helix.” DNA 只是看起来像绳子，并非说它真是如此。选项B混淆了事实与比喻。故答案为B。

2. C分析：由文章第二段可知，科学家获得了诺贝尔奖，可见其成就的重要性。尤其在最后一句明确指出他们工作的重要性，所以C正确。A不对，因为弗兰克林在获奖之前已经去世;B不对，1953年只是发现了DNA，并不意味着完全了解了其秘密;D也不对，与原文不符。故答案为C。

3. D分析：由文章第三段最后一句“The rope and steps of the DNA, they said, were made of four kinds of nucleotide bases hooked together in special ways that could carry the coded messages of life 可知答案，故答案为D。”

4. A分析：本体的答案就是第一段第一句：“Each living cell contained the message EAT, GROW, SPLIT, AND PASS THIS MESSAGE ALONG.”之所以选A,是因为它包含的内容最全面，而B, C D三个选项都仅说到了问题的一个方面，故答案为A.

5. B分析：本题考察对文章的推理。由第三段中的“… which contains the cell messages.”可知答案，双螺旋结构就是指DNA的结构。故答案为B。

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