Margaret is convinced that she received a "C" in her chemistry class instead of an "A" because of widespread cheating by her fellow students. She is sure that she must be as capable in the chemistry course as in her other subjects.

Rationalization

Explanation:

Rationalization  is defined as mechanism in which controversial behavior is justified through logical reasoning so that actual behavior can be avoided.Rational justification is made so that behavior can look correct and admirable by others.This is type of defense mechanism.

According to the question,Margaret is thinking rationally as she is justifying her low grade with logical reasoning of cheating done by her fellow classmates .She thinks she is actually good in chemistry as other subjects rather than considering that she actually needs improvement in the subject.

you should try adrenaline. it kicks in in situations like this.