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Scientist : A recently-concluded study found that owning a cat can reduce the risk of a heart attack by one-third. This was attributed to the stress relief that comes from having a cat at home. Since dogs are also usually kept as companions, owning a dog should also reduce the risk of heart attack by one-third.

All of the following weaken the conclusion except -
a. The researchers believe that the stress relief comes from the unique act of petting a cat in the lap
b. The difficulty in finding someone to watch a dog means that the dog owners are rarely able to take vacation or make visit friends and family.
c. Some people who choose cats have other elements of lower stress life while dog owners usually do not
d. Dogs often react to sounds with loud barking that prevent the owner from getting a full night's rest
e. Dogs require frequent walks that can add to an already hectic schedule