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
Step-by-step reasoning process below:

User
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. The answer: pair.
Assistant