문법 질문입니다. finding an answer 뒤에 전치사가 필요한가요?

다음 문장에서 B와 C가 틀린 이유가 궁금해요.

Aquaculture — or sea farming, as it is sometimes called — is one of the brightest hopes for finding an answer the problem of a world food shortage. Although it may be years before aquaculture will yield really large quantities of food, it is already partially successful. One of its success is the growing of oyster.

C가 틀린 건 알겠는데, B에서 어떤 부분이 잘못됐는지 설명 부탁드려요.