Which sentence uses a verb that agrees with its compound subject?

a. either those bushes or that tree are blocking the sunlight.
b. either janice or rosa are her best friend.
c. a cement mixer and a bulldozer has blocked the entrance to the street.
d. neither the terns nor the gulls have returned yet.

The sentence that uses a verb that agrees with its compound subject is D. Neither the terns nor the gulls have returned yet. When two subjects are joined by the coordinating conjunction "or" or "nor", the verb should agree with the subject closer to the verb. When they are joined by "and", the verb should agree with "they" (plural). D is correct because gulls (plural) is closer to the verb and agrees with "have".