In this sentence, which has no road signs, read for key words and what’s implied (i.e., for logic). When an “expectation of instant gratification” isn’t fulfilled, a feeling of disappointment would ensue. So the answer choices have to mean “disappointment.” You can eliminate choices (B) and (E), endearment and elation, right away since they have the opposite meaning. Choice (F) pacifism, “an opposition to war of any kind,” isn’t right for this sentence—an unreturned message would cause conflict in a relationship, rather than promote peace. Choice (C) recompense means “compensation” and can also be eliminated. That leaves (A) and (D), chagrin and vexation, both of which match the prediction and have the right meaning for the sentence.