阅读理解。 Scientists who try to predict earthquakes have gotten some new helpers recently-animals. That's right, animals. Scientists have begun to understand 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 cage. All of this unusual behavior, as well as physical changes in the earth, warned Chinese scientists of the coming quake. They moved people away from the danger zone saved thousands of lives. One task for scientists today is to learn exactly which types of animal behavior predict quakes. It's not an easy job. First of all, not every animal reacts 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 enclosure. The Australian horse next to him, however, remained perfectly calm. It's also difficult at times to tell the difference between normal animal restlessness and 'earthquake nerves.' A zoo keeper once called earthquake researchers, saying that his cougar 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 kinds 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 sense tiny changes in air pressure, gravity, or the magnetism of earth. This extra sense probably helps animals predict earthquakes. A good example of this occurred with a group of dogs. They were shut in an area that was being shaken by a series of tiny earthquakes. (Several small quakes often come before or after a large one.) Before each quake a low booming sound was heard. Each boom caused the dogs to bark wildly. Then the dogs began to bark during a silent period. A scientist who was recording quakes looked at his machine. It was acting as though there were a loud noise too. The scientist realized that the dogs had reacted to booming noise. They also sensed the tiny quake that followed it. The machine recorded both, though humans felt and heard nothing. In this case there was a machine to monitor what the dogs were sensing. Many times, however, our machines record nothing extraordinary, even though animals know a quake is coming. The animals might be sensing something we measure but do not recognize as a warning. Discovering what animals sense, and learning how they know it is a danger signal, is a job for future scientists. 1. Through the passage the writer hopes to explore ____. A. why animals send a danger signal before an earthquake B. how animals know when an earthquake is coming C. why animals not humans have a good sense of danger D. how much animals know about an earthquake 2. During an earthquake in China in 1975, ____. A. chickens refused to go out of their cage B. snakes were frozen to death in their caves C. snakes awoke from their winter sleep earlier D. cows broke their halters and escaped from their sheds 3. Which of the following is one of earthquake nerves according to the passage? A. An Arabian horse tried to escape from his enclosure. B. A cougar had an upset stomach unexpectedly. C. An Australian horse was perfectly calm. D. A cat acted very strangely in a zoo. 4. The scientists did an experiment with a group of dogs to ____. A. find out that the machine could record unusual happenings B. compare the reactions of animals and those of humans C. prove that animals could sense more than humans D. find out what exact warnings animals send