Sentence Correction

Hi Everyone,
This questions is from one of the MGMAT Cats. Maybe someone can help with the OA, as I'm not quite understanding something,


According to psychologists, many dieters subconsciously prefer 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.


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) an uncertain diet plan in terms of effectiveness: such plans allow them to believe that the supposed ineffectiveness of the plan is to blame, rather than that they lack self-control in case of failure


C) diet plans with uncertain effectiveness, which will allow them to blame the supposed ineffectiveness of the plan, rather than to lack self-control, in case of failure


D) uncertainly effective diet plans, allowing them to believe the plans that are supposedly ineffective, rather than that they lack self-control, in case of failure


E) diet plans uncertain in effectiveness; in case of failure, allowing them to believe that the plan itself is ineffective rather than that they lack self-control

OA:A

[spoiler]Can someone explain why it's appropriate to use "whose" here, as I thought whose could only used in reference to persons.[/spoiler][/spoiler]

Is it okay to write "their own self control" .. i think its redundant here ..