The correct option is C rational
Absurd means wildly unreasonable, illogical, or inappropriate. The opposite of absurd is rational, or based on or in accordance with reason or logic. Hence, Option D is correct. Among the rest of the options, correct means free from error; in accordance with fact or truth, fictional means relating to or occurring in fiction, proportional means corresponding in size or amount to something else, do not express this antonym, hence incorrect