In the sentence “I wish I could fly to the moon”, the subjunctive verb phrase is “wish”. So option “c” is the correct option as far as the sentence in the given question is concerned. Subjunctive verbs are actually used to describe the state of mind of a person. It can also be used to describe the mood of the person. This kind of verb is used to describe opinion, purpose, belief of a person involved in the sentence. It is almost similar to indicative form.