[单项选择]People once widely believed that intelligent life existed on Mars. The 19th-century discovery of what appeared to be geometric designs cut across the surface was taken as evidence. The lines were thought to have been a system of canals that had been built to irrigate the surface. It is now clear that the "canals"—perhaps the most spectacular geologic features of Mars—are natural valleys where ancient rivers once flowed. Another fragmented idea concerns the planet’’s seasonal changes in color. Once attributed to the rapid spread of some life-form, these shifts are now known to develop from the movement of fine dust in the atmosphere. By the close of the 20th century none of the many experiments conducted by spacecraft had ever found persuasive evidence of life. Nevertheless, speculation continued over the existence of some form of life, in either the present or past. In 1996 scientists discovered organic compounds and minerals in a meteorite (陨石), consisting of Martian rock, t
A. the minor geologic characteristics of Mars
B. natural valleys on the surface of Mars
C. rivers that have kept flowing since ancient times
D. a system that irrigates the whole surface

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[单项选择]People once widely believed that intelligent life existed on Mars. The 19th-century discovery of what appeared to be geometric designs cut across the surface was taken as evidence. The lines were thought to have been a system of canals that had been built to irrigate the surface. It is now clear that the "canals"—perhaps the most spectacular geologic features of Mars—are natural valleys where ancient rivers once flowed. Another fragmented idea concerns the planet’’s seasonal changes in color. Once attributed to the rapid spread of some life-form, these shifts are now known to develop from the movement of fine dust in the atmosphere. By the close of the 20th century none of the many experiments conducted by spacecraft had ever found persuasive evidence of life. Nevertheless, speculation continued over the existence of some form of life, in either the present or past. In 1996 scientists discovered organic compounds and minerals in a meteorite (陨石), consisting of Martian rock, t
A. Because the surface of Mars seemed to be geometric.
B. Because the lines were drawn across the surface of the planet.
C. Because a system of canals was thought to be there.
D. Because it was the Martians that built the canals.

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Do people stop once they have achieved something No! In life, we are always trying to do things better or having more of the same success.
Jane Fonda moved from being an Academy Award actress to a successful businesswoman. Her aerobics (有氧体操) workout videos have been sold around the world.
Athletes are constantly making greater and greater efforts to lower time for races; increase heights or distances.
The world of medicine has had its series of successes too. Christian Barnard performed several successful heart transplants. Other medical experts have achieved organ transplants. Throughout the ages, mankind has found treatment and cures for tuberculosis (肺结核), cancer, and other diseases. A cure of AIDS might soon be discovered.
Age does not seem to slow down achievers. Tina Turner at 54 is still singing with gre
A. women can be successful as well
B. beautiful actresses are likely to be successful
C. successful people are not satisfied with their achievements
D. real successful people need to stand out in more than one field

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[填空题]Why do many people dislike city life Because there are ___________.

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[填空题]Only by curing AIDS can people lengthen their life spans and improve the quality of life.

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[填空题]People’s life standards, health conditions and education have been improved by the revolution of ______.

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