Most living things undergo iwo types of biological change during their lifelime. One is 1______, an increase in the size or efficiency of an organism. The other is aging,which involves a decrease in size or efficiency.
Signs of aging begin to 2______ in most people beiween the age of 30 and 40. Heredity determines most of the ways a person changes while aging, but environment also 3______.Graying hair is probably the most common sign of aging. All the senses decline with age. For example. the eyes lose their ability to adapt 4______ darkness, and they require brighter light for reading.
Movement becomes harder with age. By age 80. about half the muscle cells have been replaced by other kinds of tissue. In women 5______, bones lose calcium and become more likely to 6______. As a person ages, the body's ability to combat infection declines. This change occurs because the white blood cells of 7______ is called the body's immune system lose their 8______ function.
Many people believe that with advancing age. an individual loses the ability to learn, remember, and make decisions. But 9______ disease or injury damages the brain, a healthy elderly person who 10______ active probably suffers no serious decline in 11______ ability.
No one completely understands the aging process. Some scientists 12______ that human aging will ever be controlled. Others believe that aging can be 13______. Usually, normal human cells can be kept 14______ in a laboratory for only a limited time. But 15 ______ cells, such as various kinds of cancer cells, can live for a long lime. If scientists can determine how such cells survive, they may gain an insighl into the process of cell aging.
1
A.to grow B.growth C.to be born D.birth正确答案B
