Pierre can produce either a combination of 20 bow ties and 30 neckties or a combination of 35 bow ties and 15 neckties. If he now produces 35 bow ties and 15 neckties, what is the opportunity cost of producing an additional 15 neckties?

(A) 2 bow ties
(B) 15 bow ties
(C) 20 bow ties
(D) 35 bow ties