C: decided they would eat only the red M&M's and avoid the rest

    Incorrect.

Belief perseverance is where older beliefs remain intact, in spite of new information that presents convincing evidence the old belief is inaccurate or irrational.  In choice C, the newer information (e.g. avoiding some red M&M's) has altered the original belief(e.g. M&M's cause cancer), contradicting research on belief perseverance.