Available options:
(a). gastropod shells.
(b). orchids.
(c). invertebrates.
(d). swamp vegetation.
(e). Most plants.
(f). insects.
(g). barnacles.
(h). animals.

Fact 1: Mollusks are a major food source for other organisms, including humans. Fact 2: Mollusks are invertebrates and are no exception. Given the two facts above, what is a major food source for other organisms, including humans?
Answer:
(c).