Animals and Earthquakes Scientists who try to predict earthquakes have got some new helpers recently-animals．
Scientists have begun to catch on to what farmers have known for thousands of years． Animals often seem to know in advance that an earthquake is coming，and they show their fear by acting in strange ways． Before a Chinese quake in 1975 snakes awoke from their winter sleep early only to freeze to death in the cold air． Cows broke their halters （缰绳） and tried to escape． Chickens refused to enter their coops． All of this unusual behavior，as well as physical changes in Earth，alerted Chinese scientists to the coming quake． They moved people away from the dangerous area and saved thousands of lives．
One task for scientists today is to learn exactly which types of animals" behavior predicts quakes． It's not an easy job． First of all，not every animal can react to the danger of an earthquake． Just before a California quake in 1977，for example，an Arabian horse became very nervous and tried to break out of his stall． The horse next to it，however，reminded perfectly calm． It's also difficult at times to tell the difference between normal animals restless and "earthquake nerves"．A zoo keeper once called earthquake researchers to say that his cougar （美洲狮） had been acting strangely． It turned out that the cat had an upset stomach!
A second task for scientists is to find out exactly what kind of warnings the animals receive． They know that animals sense far more of the world than humans do． Many animals can see，hear，and smell things that people do not even notice． Some can detect tiny changes in air pressure，gravity，or the magnetism （磁力） of Earth． This extra sense probably helps animals predict quakes．



What is the main idea of this passage？ ______

A. Animals don't know when an earthquake is coming．
B. Animals can predict earthquakes．
C. The author doesn't know whether the animals can feel the coming of an earthquake or not．
D. Human beings have to move the animals away before an earthquake is coming．

Some animals could predict earthquakes because they can detect tiny changes ______ ．

A. in the air pressure
B. in gravity
C. in the magnetism of the earth
D. all of the above

How do all the animals exactly know when an earthquake is coming？ ______

A. By their extra senses．
B. By the changes in air pressure，gravity or the magnetism．
C. People don't know exactly．
D. The passage doesn't mention it．

The author's purpose is mainly to ______ ．

A. express an argument
B. make a serious proposal
C. present a discovery
D. express suspicions