阅读短文，并按要求完成下列句子。
We know that many animals do not stay in one place. Birds, fish and other animals move from one
place to another place at a certain time. They move for different reasons: most of them move to find food
more easily, but others move to get away from places that are too crowded.
When cold weather comes, many birds move to warmer places to find food. Some fishes give birth in
warm water and move to cold water to feed. The most famous migration is probably the migration of fish,
which is called "salmon"(鲑鱼).This fish is born in fresh water but it travels many miles to salt water. There
it spends its life. When it is old, it returns to its birthplace in fresh water. Then it gives birth and dies. In
northern Europe, there is a kind of mouse. They leave their mountain homes when they become too crowded.
They move down to the low land. Sometimes they move all the way to the seaside, and many of them are
killed when they fall into the sea.
Recently, scientists have studied the migration of a kind of lobster (龙虾). Every year,when the season
of the bad weather arrives, the lobsters get into a long line and start to walk across the floor of the ocean.
Nobody knows why they do this, and nobody knows where they go. So, sometimes we know why humans
and animals move from one place to another place,but at other times we don't. Maybe living things just like
to travel.
1. Most animals move from one place to another at a certain time to _______.
A. give birth
B. enjoy warmer weather
C. find food more easily
2. The fish called "salmon" spends a long time in _______.
A. salt water
B. rivers
C. fresh water
3. The mice in northern Europe move when _______.
A. they give birth
B. the place gets too crowded
C. they haven't enough food
4. The lobsters move _______.
A. to the fresh water
B. at a certain time
C. to find more food
5. What is the main idea of the passage?
A. Animals move to find food more easily.
B. The migration of the fish called "salmon" is the most famous migration.
C. Sometimes we know why and how living things move from one place to another,but sometimes we don't.
