题目内容：

 

Before winter arrives, many kinds of birds start to fly south. People often call it migration. How much do you know about migration? Why do only some birds migrate? How do birds know when to go south? Can they find their way?

Some birds fly south because they may die from hunger if they don't do that. The woodpecker(啄木鸟),for example, doesn't need to fly south because it can find something to eat in the bark(树皮) of the trees. But some birds eat grains(谷物). Their food disappears in winter, so they must fly south where food can still be found. But why don't they stay there forever? Perhaps they know if they stay in the south, they will eat up food there, too.

Birds seem to know when winter comes because they find that the days are getting shorter in winter. Once they leave from the north, the sun is really helpful. The sun is in different positions in the sky at different time of a day. Birds know the time of the day by watching the position of the sun. On long flights, most of the birds use stars to navigate(导航) their way.

The homing pigeon(信鸽) doesn't use the sun or the stars. Scientists believe that it uses the magnetic field(磁场) of the earth. One of the most amazing migrations is that of the tiny hummingbird(蜂鸟). It travels from Canada to Mexico—a long distance of over 3600 kilometers.

1.The underlined word “migration” in the first paragraph means________

A.looking for food B.practicing flying C.moving to another place

2.The birds which eat grains fly south in winter mainly because________

A.they like warm weather better.

B.they really need food.

C.it is one of their habits.

3.On long migration flights, most birds find their way with the help of________

A.the stars B.the magnetic field C.the sun

4.Which of the following is NOT TRUE according to the passage?

A.The woodpecker doesn't need migration.

B.Many birds migrate in the middle of winter.

C.The hummingbird can fly to Mexico for food in winter.

5.What is the main idea of the passage?

A.The different ways birds use to migrate.

B.The reasons why many birds migrate in winter.

C.The mystery(奥秘) of birds' migration.