阅读理解
Migrations are one of the animal kingdom’s most widespread phenomena.They are seasonal tests of endurance，collective journeys often taken at great costs by birds，whales，land mammals，insects，and other creatures that are wired to travel.Scientists estimate that onethird to half of all animals—and even some microorganisms—migrate during part of their lives.
According to scientists, human actions are threatening many migrations.Habitat destruction，the creation of obstacles such as dams and fences，overexploitation of natural resources, and climate change are combining to make migrations increasingly difficult for many species.
Global warming，for example，is changing flowering times and other natural cycles，driving many birds and insects to move their ranges or arrive before or after their food sources have appeared. Many of the planet’s great migrations have already disappeared.
By increasing public awareness of the troubles of migratory animals and committing to the preservation not only of individual species but also their way of life，many migrations can still be saved.Migrations should be saved，if not for the absolute fear that seeing millions of animals moving with one purpose elicits，then for their ecological importance.
“What we really want to protect is the natural phenomenon of abundance，”Wilcove said.“If we wait until migrating animals are endangered，then we lose both the ecosystem benefits associated with their abundance and also the wonder and majesty(壮丽)of migrations.”
“It’s like global warming” he said.“You have to alert people，and after a while，the public knows about it and they do something about it.That’s when the big changes will come about.I think there’s absolute hope.”
When animals begin to migrate，they will________.

A．achieve it whatever is needed

B．spend half of their lives in migrating

C．make the journey in an individual way

D．adapt to the season at a fixed place

Which of the following affects flowering times?

A．Habitat destruction.

B．The building of dams.

C．Global warming.

D．The use of natural resources.

Migrations should be saved because________.

A．it is a pleasure to see millions of animals moving with one purpose

B．the way of individual species’ life should be protected

C．it is environmentally critical mass movement

D．the benefits of the ecosystem are connected with it

The attitude of Wilcove towards saving migrations is ________.

A．sympathetic

B．negative

C．suspicious

D．optimistic

What’s the passage mainly about?

A．Animals’ migrations need saving.

B．Global warming makes animals migrate more frequently.

C．Animals’ migrations are affected by their environment.

D．Migrating animals are reducing in numbers rapidly.