单选题 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 tot different reasons: most of them move to find food more easily, but others move to get away from place 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 the 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 cold, 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. 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.

单选题 The majority of animals migrate for ______.

A. place
B. safety
C. food
D. warmth

【正确答案】 C

【答案解析】[解析] 根据“most of them naove to find food more easily”可知，动物的迁徙主要是为了寻找食物。

单选题 Salmon is known as a creature spending most of its life in ______.

A. warm water
B. fresh water
C. cold water
D. salt water

【正确答案】 D

【答案解析】[解析] 根据“The most famous migration is...travels many miles to salt water”可知大马哈鱼会穷其一生从淡水河迁往海中。

单选题 Mice in northern Europe go away from homes when ______.

A. they are short of food
B. there is not enough space
C. it's getting warmer in the low land
D. it's getting colder in the mountains

【正确答案】 B

【答案解析】[解析] 根据“In northern Europe, there is a kind of mouse. They leave their mountain homes when they become too crowded. ”中的crowded可知，住宅中已经没有足够的地方供老鼠生存了。

单选题 The reason why the lobsters migrate is ______.

A. the bad weather
B. the depth of the ocean
C. scientists' lack of interest
D. unknown

【正确答案】 D

【答案解析】[解析] 根据“Nobody knows why they do this, and nobody knows where they go. ”可知，没有人知道龙虾为什么要迁徙，要迁往何处。

单选题 The passage is mainly about ______.

A. living thing on the move
B. the most famous migration
C. mice in northern Europe
D. migrating of lobsters

【正确答案】 A

【答案解析】[解析] 文章一开头就点出主题“We know that many animals do not stay in one place. ”接下来对动物的迁徙进行了描述和分析，由此可以判断文章的标题应选A。