3.Black Americans are， on the whole， about twice as likely as White Americans to develop high blood pressure. This likelihood also holds for westernized Black Africans when compared to White Africans. Researchers have hypothesized that this predisposition in westernized Blacks may reflect an interaction between western high-salt diets and genes that adapted to an environmental scarcity of salt.

　　Which of the following statements about present-day， westernized Black Africans， if true， would most tend to confirm the researchers' hypothesis？

　　（A） The blood pressures of those descended from peoples situated throughout their history in Senegal and Gambia， where salt was always available， are low.

　　（B） The unusually high salt consumption in certain areas of Africa represents a serious health problem.

　　（C） Because of their blood pressure levels， most White Africans have markedly decreased their salt consumption.

　　（D） Blood pressures are low among the Yoruba， who， throughout their history， have been situated far inland from sources of sea salt and far south of Saharan salt mines.

　　（E） No significant differences in salt metabolism have been found between those people who have had salt available throughout their history and those who have not.

　　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？

　　（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.