Let's think step by step! What are a source of food for many fish species?\nOptions:\n- (A) layers of fat\n- (B) bird species\n- (C) human species\n- (D) keystone species\n- (E) Organic compounds\n- (F) barnacles\n- (G) gastropod shells\n- (H) species of deer
The thinking starts now:
User
Sponges are a source of food for many species of fish. Sponges are also keystone species. Keystone species are a source of food for many fish species. The final answer: (D).
Assistant