Sentence Correction (SC) | Re: According to psychologists, many dieters subconsciously

According to psychologists, many dieters subconsciouslyprefer a diet plan whose effectiveness is uncertain -- a consideration that, in case of failure, lets them blame the supposed ineffectiveness of the plan rather than their own lack of self-control.

Please provide the Explanations if possible.

A )a diet plan whose effectiveness is uncertain -- a consideration that, in case of failure, lets them blame the supposed ineffectiveness of the plan rather than their own lack of self-control
B)