Passage Four Public health experts have long been skeptical about the beneficial effect of pets on the health of their owners. After all, dogs bite and pass on parasites, and pigeons and parrots cause lung disease. However, in 1991, researchers at the University of Cambridge in Britain discovered that a short time after acquiring a cat or a dog, some people suffer less from health problems such as headache, backache and flu. It was also announced recently that Australians who keep pets tend to have less cholesterol in their blood than non-pet owners with comparable lifestyles, them less likely to develop heart disease. For the time being, the findings are little more than puzzling correlations. Why should owning a pet make you less likely to suffer from backache Why should it reduce your cholesterol level Many researchers suspect that answers will be found in the subtle links between mental and physical well-being. If the newly discovered correlations between human health and pet ownership can be confirmed, they are likely to trigger fresh research on the psychological and physiological effects of keeping pets. The hint that pets could help some people to live longer came from a discovery made over a decade ago. Erica Friedmann, working at the University of Maryland in the United States, investigated whether a person’ s social life and degree of social isolation might influence their ability to survive a heart attack. Friedmann interviewed 92 recovering male patients and quizzed them in detail about their lifestyle, a few questions touching upon pets. A year later four of the 92 men had died. Friedmann went back to her data to look for differences between those who had and those who had not survived. She found that socially isolated people were more likely to fall victim, and that those who had pets were more likely to recover. Or the explanation is that pets can provide owners with a special kind of emotional support which is lacking or at least uncommon in relationships between people. An animal’ s muteness is a benefit, not a burden. The problem with language is that although we use it to communicate the deepest thoughts and emotions, we also use it to deceive, misinform, criticize and insult others. The fact that pets listen and seem to understand, but do not question or evaluate, may be one of their most endearing assets as companions. It resembles the relationships some psychotherapists try to build. Questions 16-20 are based on Passage Four. For a long time doctors have been doubtful if __________ .