A、The polluted fish killed 3,000 of them. B、Insects poisoned so many of them. C、Pollution greatly reduced their number. D、Pestic

In 1782，soon after the United States won its independence, the bald eagle was chosen as the national bird of the new country. American leaders wanted the eagle to be a symbol of their country because it’s a bird of strength and courage. They chose the bald eagle because it is found all over North America and only in North America.
    But a little over 200 years later, the bald eagle had almost disappeared from the country. And in 1972, there were only 3000 bald eagles in the entire United States. The reason for the birds’ decreasing population was pollution, especially pollution of the rivers by pesticides. Pesticides are chemicals used to kill insects and other animals that attack and destroy crops. Unfortunately, rain often washes pesticides into rivers. Pesticides pollute the river and poison the fish. Eagles eat this fish and poison affects their eggs. The eggs are very thin shells and do not hatch. Eagles lay two or three eggs a year because many of the eggs do not hatch that produce more eagles. The number of eagles quickly becomes smaller.
    Today, the American government and the American people are trying to protect the bald eagle. The number of bald eagles is increasing. It now appears that the American national bird will survive and remain a symbol of strength and courage.
Question 1: What made the bald eagle the national bird of the USA?
Question 2: What happened to bald eagles?
Question 3: What is true about the bald eagle?