Critical Reasoning

Hi....
I am confused between option C & D. Kindly help

Doctor: Research shows that adolescents who play video games on a regular basis are three times as likely to develop carpal tunnel syndrome as are adolescents who do not play video games. Federal legislation that prohibits the sale of video games to minors would help curb this painful wrist condition among adolescents.

The doctor's conclusion depends on which of the following assumptions?


A) The majority of federal legislators would vote for a bill that prohibits the sale of video games to minors.

B) Not all adolescents who play video games on a regular basis suffer from carpal tunnel syndrome.

C) Playing video games is the only way an adolescent can develop carpal tunnel syndrome.

D) Most parents would refuse to purchase video games for their adolescent children.

E) The regular playing of video games by adolescents does not produce such beneficial effects as better hand-eye coordination and improved reaction time.

Premise: Adolescent who play video games regularly develop X compared to adolescents who do not play video games.
Conclusion: Federal legislation would help from coming out this situation - not developing X.

A is not assumption, it is the conclusion.
If B is the assumption, the conclusion is invalid, if not all adolescents who play video games suffer from the syndrome, then federal legislation cannot help here.
C says, playing video games is the only way to develop the syndrome. If we negate it, playing video games is not the only way. So if there are other ways, federal legislation cannot help here also. Negating C, makes conclusion invalid. So C is the assumption.
D says, most parents would refuse. If we negate, few parents would refuse, but few is not no. So D is not the assumption.
E is out of scope.

According to my understanding also "c" must be the answer.
This is a question from one of the Manhattan CAT's and the answer given is "D".