A、They often frighten their owners. B、They make a lot of trouble for their owners. C、They bring disasters to their owners. D、The

More than sixty percent of all homes in the United States have at least one thing in common: the people living in them keep one or more small animals as pets. These pet owners spend about ten billion dollars each year to buy, feed’ and care for their animals. Why? If you ask the owners, their answers probably would be emotional.
     During the past ten years researchers have been attempting to find a more scientific answer. Much of the research on the ties between people and pets is being done at the University of Pennsylvania. Re searchers there have watched hundreds of people play with small animals. Some were very sick. Perhaps the most important observation was the physical effect the animals had on most of the people. The animals seemed to calm the people who touched and talked to them.  The human’s blood pressure actually dropped.