GMAT Critical Reasoning (CR) | A nationwide study of sibling rivalry shows that brothers and sisters

A nationwide study of sibling rivalry shows that brothers and sisters continue to compete throughout their lives. The majority of those who volunteered to be interviewed for the study convinced the researchers that many of their daily actions were caused by sibling rivalry.

If true, which of the following most weakens the findings stated above?

A) Short interviews tend to be less reliable than long interviews.
The lenght of the interview is out of scope.
B) Rivalry between sisters is more intense
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