托福阅读真题+题目+答案：Dams and Flood Control
There are both advantages and disadvantages to building dams on rivers. On the one hand, dams can be beneficial to human populations. They provide reserves of fresh water, a commodity crucial to life, both directly as drinking water and indirectly because irrigating farmland provides crops for food. Moreover, the energy of water flowing through dams can be harnessed to provide electricity. The location of dams on rivers also enables flooding to be controlled. Thus dams can provide protection from the extremes of the local climate. Heavy rains in headwater areas, which might otherwise lead to downstream flooding, are impounded in the reservoir(water storage area) behind a dam. By the same token, during dry periods that might otherwise produce drought, water can be released from the reservoir to downstream areas.
1. Paragraph 1 supports which of the following ideas about dams?
A They tend to be located far from areas where food crops are grown.
B They can be used to increase the amount of water flowing downstream as well as to decrease it.
C They function most effectively in areas that do not regularly experience extremes of climate.
D Their indirect advantages are more valuable for human populations than their direct advantages are.
2. According to paragraph 1, dams prevent floods by
A preventing excess water from collecting in headwater areas
B releasing excess water from reservoirs to downstream areas
C channeling excess water into drier areas
D enabling excess water to be contained in reservoirs
On the other hand, introducing a dam into a river system will alter the structure of the river. Sediment will be deposited upstream of the dam and in the reservoir (reservoirs are inevitably only transient features and will ultimately fill up with sediment). Downstream, increased erosion will occur. Landscapes and ecosystems are submerged beneath the new reservoir. The dam itself represents a potential hazard should it ever fail. The collapse of the St. Francis Dam in southern California in 1928 was the consequence of building it against a weak rock support only two years earlier.
3. The author mentions the “collapse of the St. Francis Dam in southern California in 1928” in order to
A provide an example of a dam design in the 1920s
B point out a specific way in which a dam can alter the structure of a river
C support the idea that there is a risk of dams failing
D support the claim that reservoirs are transient features
Government policies in the United States regarding the construction of dams have shifted considerably in the past century. The early part of the twentieth century saw an enormous boom in dam construction, particularly in the arid West. In recent years this trend has been halted and even reversed in some cases, as plans to tear down dams and restore stream systems to their natural state are under consideration. Any discussion of the construction of a dam across a "wild" river usually pits conservationists against power companies and farmers. One side stresses the need to conserve for future generations; the other stresses the needs of the modern population and economy. The example of the Trinity River Dam in northern California serves to illustrate many of the issues at work here.
托福阅读真题+题目+答案：Dams and Flood Control，完整一篇下载，10元有偿！