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4.Two decades after the Emerald River Dam was built， none of the eight fish species native to the Emerald River was still reproducing adequately in the river below the dam. Since the dam reduced the annual range of water temperature in the river below the dam from 50 degrees to 6 degrees， scientists have hypothesized that sharply rising water temperatures must be involved in signaling the native species to begin the reproductive cycle.

Which of the following statements， if true， would most strengthen the scientists' hypothesis？ www.51lunwen.org 

（A） The native fish species were still able to reproduce only in side streams of the river below the dam where the annual temperature range remains approximately 50 degrees.

（B） Before the dam was built， the Emerald River annually overflowed its banks， creating backwaters that were critical breeding areas for the native species of fish.

（C） The lowest recorded temperature of the Emerald River before the dam was built was 34 degrees， whereas the lowest recorded temperature of the river after the dam was built has been 43 degrees.

（D）Nonnative species of fish， introduced into the Emerald River after the dam was built， have begun competing with the declining native fish species for food and space.

（E） Five of the fish species native to the Emerald River are not native to any other river in North America.

5. An advertisement designed to convince readers of the great durability of automobiles manufactured by the Deluxe Motor Car Company cites as evidence the fact that over half of all automobiles built by the company since 1970 are still on the road today， compared to no more than a third for any other manufacturer.

Which of the following， if true， most strongly supports the advertisement's argument？

（A） After taking inflation into account， a new Deluxe automobile costs only slightly more than a new model did in 1970.

（B） The number of automobiles built by Deluxe each year has not increased sharply since 1970.

（C） Owners of Deluxe automobiles typically keep their cars well maintained.

（D） Since 1970， Deluxe has made fewer changes in the automobiles it manufactures than other car companies have made in their automobiles.

（E） Deluxe automobiles have been selling at relatively stable prices in recent years.
6.Six months or so after getting a video recorder， many early buyers apparently lost interest in obtaining videos to watch on it. The trade of businesses selling and renting videos is still buoyant， because the number of homes with video recorders is still growing. But clearly， once the market for video recorders is saturated， businesses distributing videos face hard times.

Which of the following， if true， would most seriously weaken the conclusion above？

（A） The market for video recorders would not be considered saturated until there was one in 80 percent of homes.

（B） Among the items handled by video distributors are many films specifically produced as video features.

（C） Few of the early buyers of video recorders raised any complaints about performance aspects of the new product.

（D） The early buyers of a novel product are always people who are quick to acquire novelties， but also often as quick to tire of them.

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