GMAT Critical Reasoning (CR) | Re: A recently-completed study found that owning a cat

Scientist: A recently-completed study found that owning a cat can reduce the risk of a heart attack by one-third. This finding was attributed to the stress relief that comes from having a cat in the 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 scientist's hypothesis EXCEPT:

A. The researchers believe that the stress relief comes from the unique act of petting a cat held in the lap.
This
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