听力原文： More than 50 percent of all homes in the U.S. have one thing in common people living in them keep one or two small animals as pets. In fact there are more pets in the U.S than children. Why? Researchers have been attempting to find the scientific answer to this question. Much has been written about how animals, violent crimes, and about how they help children deal with emotional problems. Last year researchers met at the America's National Institute of Health. They found there is a lot of evidence that animals may be helpful to human health. But they agreed more work is needed to show and measure these facts in a scientific way. Recent studies have confirmed an animal coming effect. For example, a research at a government laboratory near Washington examined how animals influence blood pressure and heart rote. The study involves 92 students. All were in good health. Each one met with a dog whom they did not know but who was friendly. The students were permitted to touch or hold the dog. The researchers measured the students' blood pressure and heart ram before and during the meeting. The results showed an overall drop in blood pressure and heart rate after the students talked to the dog. The researcher said the same effect often takes place in the animal itself.. Other students have shown that different people react differently to animals. The good effects of pets on physical and mental health may be linked to a person's position within a social or economic group. Researchers say they still do not fully understand the physical changes that take place when humans and animals are together, but they say it is clear that animals fill a human need. Animal pets don't reject people because they are sick or disabled. As a result, they may provide the sick or the disabled with a better sense of security. (30)