Passage Two
14.
A) It limited their supply of food.
B) It made their eggshells too fragile.
C) It destroyed many of their nests.
D) It killed many baby bald eagles.

15.
A) They found ways to speed up the reproduction of bald eagles.
B) They developed new types of feed for baby bald eagles.
C) They explored new ways to hatch baby bald eagles.
D) They brought in bald eagles from Canada.

16.
A) Pollution of the environment.
B) A new generation of pest killers.
C) Over-killing by hunters.
D) Destruction of their natural homes.

答案及参考原文：

BDD

America's National Symbol – the Bald Eagle almost went extinct 20 years ago. But it has made a comeback. In fact, the US Fishing and Wildlife Service is considering the possibility of taking it off the endangered species list. Once, more than 50,000 pairs of bald eagles nested across the country. But by 1960, that number had fallen below 400. The chief killer was the widely used DDT. Fish soaked up DDT died and were washed up on shores where bald eagles feasted on them. DDT prevented eagle eggshells from thickening. The shell became so thin that they shattered before the babies hatched(14). Fortunately in 1972, a law was passed to ban DDT, which saved the bald eagle from total wipeout. And since then wildlife biologists have reintroduced bald eagles from Canada to America(15). The result was that last year US bird watchers counted 11,610 bald eagles in the country. If it were dropped from the endangered list, the bald eagles would still be a threatened species. That means the bird would continue to get the same protection. No hunting allowed, and no disturbing of nests. But bald eagles still face tough times. The destruction of their natural homes could be the next DDT causing eagle numbers to drop quickly(16).

14. What was the main harmful effect of the pest-killer DDT on bald eagles?
15. What measure did the wildlife biologists take to increase the number of bald eagles?
16. According to the speaker, what is the possible danger facing bald eagles?