Choose the right answer to fill in the blank.
If he ____________ a horse he would fly.
If he were a horse he would fly.
An unreal conditional sentence expresses events that are hypothetical or contrary-to-fact. Some "if" clauses use "were" even if the pronoun is singular. In these statements, the writer is specifying an event is impossible in the present or did not happen in the past. Accordingly, the option, If he were a horse he would fly, is the correct use.