We know that many animals do not stay in one place.Birds,fish and other animals move from one place to another 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（迁移）is probably the migration of fish,which is called “Salmon”.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 there.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 bad weather arrives,the lobsters get into a long time 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,but at other times we don’t.Maybe living things just like to travel.
Most animals move from one place to another at a certain time to _________.

A．give birth	B．enjoy warmer water
C．find food more easily	D．find beautiful places

The mice in northern Europe move when _________.

A．they give birth	B．the weather is bad
C．the place gets too crowded	D．they haven’t enough food

The lobsters move _________.

A．to the fresh water	B．to the deeper sea
C．at a certain time	D．to find more food