阅读理解 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.

单选题 What is the main topic of the passage?

【正确答案】 A

【答案解析】主旨题型。见本文主旨句，第二段第一句：The study of isolated roots has provided an understanding of the relationship between shoots and roots in intact plants．(第一段谈的是the study of isolated roots；第二段谈的是the relationship between shoots and roots)；因此选项A应为答案。

单选题 The word "themselves" in Paragraph 1 refers to________.

【正确答案】 A

【答案解析】细节题型。见第一段第一句：About fifty years ago，plant physiologists set out to grow roots by themselves in solutions in laboratory flasks．这里指plant physiologists自己培育根用作物；因此themselves在此应为正确选项。

单选题 The scientists found what the isolated roots need is________.

单选题 Roots have the ability to________.

单选题 According to the passage, what is ATP?

【正确答案】 C

【答案解析】推断题型。第一段提到(块)根需要sugar and the usual minerals and vitamins，但不需要organic nitrogen compounds，因(块)根可自造所需的蛋白质和其它organic compounds；这里反复提到的organic compounds应包括the high energy compound ATP(见第一段倒数第二句)；因此可推断出选项C(一种化合物)为答案。

单选题 The word "intact" in Paragraph 2 is closest in meaning to________.

【正确答案】 C

【答案解析】词义题型。本句意为：对于分离出(孤立)的根所做的研究为了解根和芽作为一植物......的关系提供了帮助。当然intact应为：包括根和芽的植物整体；因此选项C为答案。

单选题 The use of the phrase "comes in handy" in Paragraph 2 indicates that the process is________.

【正确答案】 C

【答案解析】词义题型。见第二段第四句：This comes in handy for the growth of buds in the early spring when leaves are not yet functioning．这对于芽(蓓蕾)在早春的生长很是必要，因为叶在那时还没有起作用。所以comes in handy应表“必要”，所以选项C为答案。

单选题 It can be inferred from the passage that, in the early spring, the buds of plants________.

【正确答案】 D

【答案解析】推断题型。见第二段第三、四句：根为芽提供有机氮，这对于芽(蓓蕾)在早春的生长很是必要，因为叶在那时还没有起作用。因此可推断出：在那时，植物的芽是从根处获得有机化合物的；所以选项D为答案。

单选题 Which of the following best describes the organization of the passage?

【正确答案】 C

【答案解析】主旨题型。第二段第一句为本文的主旨。而这是植物生理学家通过研究种植在实验瓶中的根，及在此基础上研究根、芽作为植物整体间的关系取得的；本文对此作了较详尽的解释。因此选项C为答案。

单选题 Where is this passage likely to be found?

【正确答案】 B

【答案解析】推断题型。根据本篇文章的结构和文体，不可能是一篇时事通讯(因发生在大约50年前)，也不会是一篇故事或小说；在此只可能是发表在一份专业刊物上，因此选项B为答案。