Explanation

Part (c), 'whomever', contains the error. Within the clause 'whoever must accept it', the pronoun functions as the subject of the verb 'must accept', so the subjective-case form 'whoever' is required. 'Whomever' is the objective case, used only when the pronoun is the object of a verb or preposition. The preposition 'to' governs the entire clause, not the pronoun directly. Hence 'whomever' must be replaced with 'whoever', and option (C) is correct.