Concept:Verbs like "believe" are stative verbs. They describe a state, not an action. Stative verbs are not used in continuous tenses.Explanation:The sentence "I don't believe him" uses the simple present tense. This is correct for a general statement about a current belief.The sentence "I am not believing him" uses the present continuous tense. Stative verbs do not take continuous forms. This sentence is grammatically wrong.Therefore, only option A is correct. Option B is incorrect because "believe" cannot be used in the "-ing" form here.Answer:A. I don't believe him.