题目内容：

    North America's birds are disappearing from the skies at a rate that's shocking even to ornithologists （鸟类学家）.Since the 1970s, the continent has lost 3 billion birds, nearly 30% of the total, and even common birds such as sparrows and blackbirds are in decline, U.S. and Canadian researchers report this week online in Science. The findings raise fears that some familiar species could go the way of the passenger pigeon, a species once so abundant that its extinction in the early 1900s seemed unthinkable.

The results, ever done to North American birds, point to ecosystems in disorder because of habitat loss and other factors, researchers say. Yet ecologist Paul Ehrlich at Stanford University, California sees some hope in this new bad news: “ It might encourage needed action in view of the public interest in our feathered friends. ”

In past decades, Ehrlich and others have recorded the decline of particular bird groups, including migratory songbirds. All together, they studied 529 bird species, about three-quarters of all species in North America, accounting for more than 90% of the entire bird population. Rosenberg and his colleagues report Grassland birds have declined by 53% since 1970—a loss of 700 million adults in the 31 species studied. Habitat loss may be to blame.

The familiar birds that flock by the thousands in suburbs were not exempt（例外）. “There's a decline of the numbers of common birds,” Rosenberg says. His team determined that 19 common species have each lost more than 50 million birds since 1970. Twelve groups, including sparrows, warblers, finches, and blackbirds, were particularly hard hit. Even introduced species that have increased in North America, such as starlings and house sparrows, are losing ground.

1.What is happening to North America's birds?

A.Most of them are dying out. B.Some of them are decreasing.

C.They are disappearing quickly. D.They are raising fears to humans.

2.What does Paul Ehrlich mean?

A.The bad news will bring interest to the birds.

B.The bad news might alarm people to take action.

C.North America's birds need our help.

D.North America's birds suffered great loss.

3.What is the last paragraph mainly about?

A.Some common birds are also decreasing.

B.Some birds die from losing their habitat.

C.The research team found some unusual things.

D.The research team studied birds in North America.

4.In which section of a website may this text appear?

A.Environment. B.Health.

C.Education. D.Science.