The first sentence is the question and the second and third are the answers. The third sentence says that the person already ‘went this morning’ and so the action that ‘going’ has already happened. So, the second sentence, being related to the third sentence, is also about the action that has already happened recently. This makes the second sentence to be one of present perfect tense. The present perfect is made using the auxiliary verb 'have/ has' plus the 'past participle' of the main verb. Hence, Option C is the correct answer as it uses past participle of the verb “be,” i.e. “been” as required by the present perfect tense of the sentence. The helping verb ‘have’ is already contained in the first sentence as its short form ‘ve’ with ‘I.’.
Options B and D cannot be used as it is not the past participle of the verb.
Option A cannot be used as it would make the sentence grammatically incorrect.