题目内容
B. Just
C. Still
D. Yet
Like distance runners on a measured course,all of us will move through time in a roughly predictable pattern.
In the first stage of our lives,we develop and grow, reaching toward the top of physical vitality(活力).
After we grow up,however, the body begins a process of gradually wearing out.
A new awareness of physical fitness may help lengthen our years of health and vitality,yet nothing we do will work to stop the unavoidable force of aging.
Most of the changes of aging take place deep inside the body.The lungs become less able to take in oxygen.Powerful muscles gradually lose their strength.The heart loses power and pumps less blood.Bones grow easier to break.
Finally, we meet a stress,a stress that is greater than our physical resistance.Often,it is only a minor accident or chance infection(a disease caused by virus),but this time,it brings life to an end.
In 1932,a classic experiment nearly doubled the lifetime of rats,simply by cutting back the calories in their diet The reason for the effect was then unknown.
Today, at the University of California at Berkley, Dr.Paul Seagle has also greatly lengthened the normal lifetime of rats.The result was achieved through a special protein limited diet,which had a great effect on the chemistry of the brain.Seagle showed that within the brain,specific chemicals control many of the signals that influence aging.By changing that chemical balance,the clock of aging can be reset.
For the first time, the mystery of why we age is being seriously challenged.Scientists in many fields are now making striking and far-reaching discoveries.
An average lifetime lasts 75 years,yet in each of us lies a potential for a longer life.If we could keep the vitality and resistance to disease that we have at age twenty, we would live for 800 years.
1.What does the underlined word “it” refer to?
A.Physical vitality. |
B.Stress. |
C.Aging. |
D.Physical resistance. |
2.Which of the following is not a change of aging?
A.People gradually lose their muscle strength. |
B.Bones tend to break more easily. |
C.The heart loses power and pumps less blood. |
D.The lungs become unable to take in oxygen. |
3.The author believes the following except that .
A.human's life pattern is predictable |
B.physical fitness can't stop the force of aging |
C.human's lifetime will last longer than 75 years |
D.all of the changes of aging take place deep inside the body |
4.How did Dr.Paul Seagle lengthen the lifetime of rats in his experiment?
A.By keeping their physical fitness. |
B.By cutting the calories in their diet. |
C.By resetting their clock of aging. |
D.By limiting the protein in their diet. |
5.What is probably the best title for the article?
A.Two Great Experiments |
B.The Mystery of Human Life |
C.The Breakthrough in the Study of Aging |
D.Ways to lengthen Human Life |
ABCD请按实际情况填写。其他请参照下表填写。
A, B, C, D, E(AB), F(AC)
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 flowers for a week or more without floral preservatives(which contain biocides that kill bacteria 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(康乃馨) retain their freshness eight times longer when kept at 12℃ than when kept at 26℃. 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, 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.