John bought a new bookend for a shelf, but he was frustrated because he forgot that they were supposed to come in what?\nOptions:\n- pair\n- a box\n- library book\n- school library\n- library holding books together
Reason slowly and give your answer.
pair
Bookends usually come in a pair.

Bookends are used to arrange the books next to each other.

Only a pair of bookends can prevent the books from falling.

.

Thus, the answer is pair