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Keeping Cut Flowers 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.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 longer when kept at 12oC than when kept at 260c. Keeping freshly harvested flowers at the right temperatures 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 attract 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 colour. 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 rate at which flowers die By controlling respiration. How is respiration controlled By controlling temperature. We know that respiration produces heat, but the reverse 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 (含氯漂白剂) can be used in small quantities. It is recommended that 15 drops of chlorine bleach(at 4% solution) be added to each litre of water. The water and solution should also be replaced each day. Paragraph 5（）
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Passage 3 Questions 11 to 15 are based on the following passage:The vitamins necessary for a healthy body are normally supplied by a good mixed diet (饮食) , including a variety of fruits and green vegetables. (79) It is only when people try to live on a very restricted diet that it is necessary to make special provision to supply the missing vitamins.An example of the dangers of a restricted diet may be seen in the disease known as “beri-beri”. (80) It used to distress large numbers of Eastern peoples who lived mainly on rice. In the early years of this century, a scientist named Eijkman was trying to discover the cause of “beri-beri”. At first he thought it was caused by a germ. He was working in a Japanese hospital, where the patients were fed on polished rice which had the outer husk (外壳) removed from the grain. It was thought this would be easier for weak and sick people to digest.Eijkman thought his germ theory was confined when he noticed the chickens in the hospital yard, which were fed on leftovers (剩饭) from the patients’ plates, were also showing signs of the disease. He then tried to isolate the germ, but his experiments were interrupted by a hospital official, who declared that the polished rice, even though left over by the patients, was too good for chickens. It should be recooked for the patients, and the chickens should be fed on cheap rice with the outer layer still on the grain.Eijkman noticed that the chickens began to recover on the new diet. He began to consider the possibility that eating unpolished rice somehow prevented or cured "beri-beri" -- even that a lack of some element in the husk might be the cause of the disease. Indeed this was the case. The element needed to prevent “beri-beri” was shortly afterwards isolated from Ace husks and is now known as vitamin B. Nowadays, this terrible disease is much less common thanks to our knowledge of vitamins. The chemical substance missing from polished rice（）
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