gre写作辅导：写作资料句子23

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8. 科技和社会变化
Inventions affect the size of populations, which in turn influences the course of history. Some inventions affect population directly: Improvements in sanitation, the development of cured for fatal illnesses, and more effective contraceptive techniques are examples. Some inventions can also have indirect effects on population: techniques that improve crop yields or permit long-term storage of food surpluses make it possible to support a larger population with a given amount of farmland. And improvements in military technology have had dramatic effects on the conduct of war and hence on population size.
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9．对能量的要求
+ t6 ]+ k3 f$ v% J  x/ J) iThroughout human history a central aspect of technological change has been the quest for new sources of energy to meet the needs of growing populations. That quest has given rise to a succession of energy technologies, each more sophisticated than the last.(animal power---steam-driven machines---internal-combustion engine---nuclear energy---fusion reaction, in which hydrogen atoms are fused into helium.)

5 H% R$ c/ ^5 l+ F5 d' w$ n4 LMany people believe that societies can meet their growing energy needs by continually investing in more sophisticated technologies. This approach has led to the development of huge nuclear-power plants to replace oil-fueled generators, and it is widely hoped that investment in fusion, an even more complex technology, will eliminate the dangers posed by nuclear power.

! w. t5 J8 F# h2 ~The trend toward greater use of nuclear power to generate electricity has become a major social and political issue. Underlying the conflict over the safety of nuclear-power plants is the issue of control.