Answer:
A - Cognitive Dissonance.
Step-by-step explanation:
As the exercise exemplifies, the theory that explains the feelings that Hai is feeling is the Cognitive Dissonance theory. This occurs when a person has at least two contradictory ideas, beliefs, values, etc, and, upon realizing of this, experiences stress. Hai believes a certain supplement will reduce his risk of cancer. Then, after years of taking them, he reads that this drug does not, in fact, reduce cancer risk. Therefore, he experiences stress, disconfort, given that the new evidence clashes against what he believes or used to believe.