B4

‘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 is one of the strongest birds.
(past simple passive, т.к. он был выбран, а не он выбрал. Определённый момент в прошлом.)

CHOOSE

B5

Today the bald eagle almost has disappeared from the country.
(present perfect, т.к. они почти исчезли и продолжают исчезать. Процесс не окончен)

DISAPPEAR

B6

In 1972 there were only 3,000 bald eagles in the entire United States. 
(past simple, т.к. мы говорим об определённом времени в прошлом)

BE

B7

The reason for the bird' s decreasing population is pollution, especially pollution of the rivers by pesticides.
(уменьшение)

DECREASE

B8

Pesticides poison the fish. Eagle eat these fish and then the eggs eagles lay have very thin shells and don’t hatch.
(present simple, т.к. это общее утверждение)

NOT HATCH

B9

Today, the American government and the American people are trying to protect the bald eagle.
(present continuous, т.к. действие происходит в настоящий момент)

TRY

B10

We are sure that the American national bird will remain a symbol of strength and courage for many years to come.
(future, останутся)

REMAIN