A、If he has a pet companion. B、If he has less stress of work. C、If he often does mental calculation. D、If he is taken care of by

Science can’t explain the power of pets, but many studies have shown that the company of pets can help lower blood pressure and raise chances of recovering from a heart attack, reduce loneliness and spread all-round good cheer.
    Any owner will tell you how much joy a pet brings. For some, an animal provides more comfort than a husband/wife. A 2002 study by Karen Allen of the State University of New York measured stress levels and blood pressure in people — half of them pet owners — while they performed 5 minutes of mental calculation or held a hand in ice water. Subjects completed the tasks alone, with a husband/wife, a close friend or with a pet. People with pets did it best. Those tested with their animal friends had smaller change in blood pressure and returned most quickly to baseline heart rates. With pets in the room, people also made fewer math mistakes than when doing in front of other companions. It seems people feel more relaxed around pets, says Allen, who thinks it may be because pets don’t judge.
    A study reported last fall suggests that having a pet dog not only raises your spirits but may also have an effect on your eating habits. Researchers at Northwestern Memorial Hospital spent a year studying 36 fat people and their equally fat dogs on diet-and-exercise programs; a separate group of 56 people without pets were put on a diet program. On average, people lost about 11 pounds, or 5% of their body weight. Their dogs did even better, losing an average of 12 pounds, more than 15% of their body weight. Dog owners didn’t lose any more weight than those without dogs but, say researchers, got more exercise overall — mostly with their dogs — and found it worth doing.
Questions 26 to 29 are based on the passage you have just heard.
26. What does the passage mainly discuss?
27. When does a person with heart disease have a better chance of getting well?
28. According to Allen, why did people do better with pets around when doing stressful tasks?
29. What do researchers at Northwestern Memorial Hospital mention in the passage?