下面的短文后有2项测试任务：（1）第23—26题要求从所给的6个选项中为第2～5段每段选择l个最佳标题；（2）第27～30题要求从所给的6个选项中为每个句子确定1个最佳选项。 Keeping Cut Flowers 1 While everybody enjoys fresh cut flowers around his/her 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. 2 An important thing to remember about cut flowers is that they are sensitive to temperature. For example， studies have shown that cut carnations （康乃馨） retain their freshness eight times lon-ger when kept at 12℃ than when kept at 26℃. Keeping freshly harvested flowers at the right tem- peratures is probably the most important aspect of flower care. 3 Flowers are not intended by nature to live very long. Their biological purpose is simply to at-tract birds or insects， such as bees， for pollination （授粉）. After that， they quickly dry up and die. The process by which flowers consume oxygen and produce carbon dioxide （二氧化碳）. called respiration （呼吸）， generates 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 ot heat relative to the mass of the flower is very high. Respiration also brings about the eventualdeath of the flower. Thus the greater the level of respiration， the sooner the flower dies. 4 How， then， to control the rate at which flowers die? By controlling respiration. How is respi-ration controlled? By controlling temperature. We know that respiration produces heat， but the re-verse（相反的过程） is also true. Thus by maintaining 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， household chlorine bleach （漂白剂） can be used in small quantities. It is recommended that 15 drops of chlorine bleach （at 4% solution） be add-ed to each litre of water. The water and solution should also be replaced each day. Paragraph 2 ___________. 查看材料
A. 2 B. 3 C. 4 D. 5 E. To F. Paragraph G.Control H.Beauty I.Role J.Most K.Need L.Ways
【参考答案】
D 本段的第一句和最后一句都是该段的主题句，但是最后一句是此题的，选项D几乎是最后一句的原句重现，故选D。