About fifty years ago, plant physiologists set out to grow roots by themselves in solutions in laboratory flasks. The scientists found that the nutrition of isolated roots was quite simple. They required sugar and the usual minerals and vitamins. However, they did not require organic nitrogen compounds. These roots got along fine on mineral inorganic nitrogen. Roots are capable of making their own proteins and other organic compounds. These activities by roots require energy, of course: The process of respiration uses sugar to make the high energy compound ATP, which drives the biochemical reactions. Respiration also requires oxygen. Highly active roots require a good deal of oxygen.

　　The study of isolated roots has provided an understanding of the relationship between shoots and roots in intact plants. The leaves of the shoots provide the roots with sugar and vitamins, and the roots provide the shoots with water and minerals. In addition, roots can provide the shoots with organic nitrogen compounds. This comes in handy for the growth of buds in the early spring when leaves are not yet functioning. Once leaves begin photosynthesizing, they produce protein, but only mature leaves can "export" protein to the rest of the plant in the form of amino acids.

　　61. What is the main topic of the passage?

　　A. The relationship between a plant's roots and its shoots.

　　B. What can be learned by growing roots in isolation.

　　C. How plants can be grown without roots.

　　D. What elements are necessary for the growth of plants.

　　62. The underlined word "themselves" in Paragraph 1 refers to ______

　　A. plant physiologists B. solutions

　　C. laboratory flasks D. roots

　　63. The scientists found what the isolated roots need is ______

　　A. quite natural

　　B. sugar, minerals and vitamins

　　C. some rare vitamins

　　D. organic nitrogen compounds

　　64. Roots have the ability to ______

　　A. make proteins

　　B. obtain fresh air

　　C. produce inorganic nitrogen

　　D. carry out activities without energy

　　65. According to the passage, what is ATP?

　　A. A biochemical process.

　　B. The tip of a root.

　　C. A chemical compound.

　　D. A type of plant cell.

　　66. The underlined word "intact" in Paragraph 2 is closest in meaning to ______

　　A. mature B. wild

　　C. whole D. tiny

　　67. The use of the phrase "comes in handy" underlined in Paragraph 2 indicates that the process is ______

　　A. unavoidable B. predictable

　　C. necessary D. successful

　　68. It can be inferred from the passage that, in the early spring, the buds of plants ______

　　A. "export" protein in the form of amino acids

　　B. do not require water

　　C. have begun photosynthesizing

　　D. obtain organic compounds from the root

　　69. Which of the following best describes the organization of the passage?

　　A. The results of two experiments are compared.

　　B. A generalization is made, and several examples of it are given.

　　C. The findings of an experiment are explained.

　　D. A hypothesis is presented, and several means of proving it are suggested.

　　70. Where is this passage likely to be found?

　　A. A newsletter. B. A magazine.

　　C. A storybook. D. A novel.

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