阅读理解。
Like many other animals, swallows will fly south when the days turn cold and the leaves from trees
begin to fall. They travel many miles to find a warmer winter. This type of travel is called migration (迁徙).
Birds are animals that like to migrate a lot when it is cold. About 600 out of 9,000 kinds of birds do it.
They leave in autumn and come back during the warm spring months.
Many birds don't like the cold. They need food, but plants die and insects (昆虫) hide in winter. So,
they'll only come home the next year, when there will be plenty of food for them to eat.
But the trip is often hard and not safe. Many birds fly in groups and make noises. Cranes (鹤) fly in
groups like the letter V, or in a row. Others travel in pairs or alone.
Some can travel a very long way. They fly between lands. For example, the Arctic tern (北极燕鸥)
can travel 20,100 kilometres. They build a home near the North Pole (北极), go to the Antarctic (南极洲)
in autumn, and then come back in spring.
How do the birds find their way? They look at things like the sun, moon and stars. They never get lost.
阅读短文，根据短文内容填表（每空不超过三个单词，最后一空为开放性试题，可多于三个单词）：
| What is migration? |
It's when animals travel from cold places to find a 1.____.
They leave in 2.____ and come back in 3.____. |
| Why do birds migrate? |
Because plants 4.____ and animals 5.____. There's not much 6.____
for them during cold winters. |
| How do birds migrate? |
The trip is often 7.____ and dangerous. Many travel in 8.____
and 9.____. |
| How do birds find their way? |
They find their way by looking at the 10.____, 11.____ and 12.____. |
What can we learn from birds'
migration? |
Animals are born naturally to be able to 13.____. |