The correct option is C To be ironed
A form of the verb “To be” is combined with a past participle to form the passive. Passive verb constructions are useful when the subject of an action is not as important as what the subject did (the action of the sentence). Here, the action of ironing is more important than who irons it. Hence th verb form is "to be ironed". Hence, Option C is correct. The rest of the options do not adhere to this rule, hence, incorrect.