题目内容：

根据短文内容, 从下框A~F选项中选出能概括每段主题的最佳选项，并在答题卡上将该选项涂黑。选项中有一项为多余项。

 

A. Control of respiration

B. Basic tips for preserving cut flowers

C. Role of respiration

D. Most important aspect of flower care

E. Need for clean water

F. Ways of stopping respiration

 

1.______________

While everybody enjoys fresh cut flowers around his house, few people know how to keep them for as long as possible. This may be done by keeping in mind a few simple facts. The key to keeping fresh cut flower for a week or more without preservatives ( which contain biocides (杀虫剂) that kill bacterial and fungus) is to keep the water fresh and the stems free of air pockets so they can continue to draw up water.

2._____________

  An important thing to remember about cut flowers is that they are sensitive to temperature. For example, studies have shown that cut carnations retain their freshness eight times longer when kept at 12℃ than when kept at 26℃. Keeping freshly harvested flowered at the right temperatures is probably the most important aspect of flower care.

3._____________

  The process by which flowers consume oxygen and produce carbon dioxide, called respiration (呼吸), supplies the energy the flower needs to give the flower its shape and color. The making of seeds also depends on this energy. While all living things respire, flowers have a high level of respiration. A result of all this respiration is heat, and for flowers the level of heat relative to the mass of the flower is very high. Respiration also brings about the eventual death of the flower. Thus the greater the level of respiration, the sooner the flower dies.

4.______________

  How, then, to control the speed at which flowers die? By controlling respiration. How is respiration controlled? By controlling temperature, we know that respiration produces heat, but the reverse ( 反面 ) is also true. Thus by keeping low temperatures, respiration is reduced and the cut flower will age more slowly.

5._____________

  Another vital factor in keeping cut flowers is the quality of the water in which they are placed. Flowers find it difficult to “drink” water that is dirty or otherwise polluted. Even when water looks and smells clean, it almost certainly contains harmful substances that can endanger the flowers. To rid the water of these unwanted substances, chlorine bleach ( 含氯漂白剂 ) can be used in small quantities. It is recommended that 15 drops of chlorine bleach be added to each liter of water. The water and solution （ 溶液 ）should also be replaced each day.