Use reasoning to answer the following question.
What is a major food source for humans?\nOptions:\n- (A) poison dart frogs\n- (B) honeybees\n- (C) barnacles\n- (D) intervertebrates\n- (E) other humans\n- (F) photosynthesis\n- (G) the body's largest organ\n- (H) Most plants

(D)
Mollusks are a major food source for other organisms, including humans.

Mollusks are invertebrates and are no exception.

Intervertebrates are a major food source for other organisms, including humans.

.

Therefore, the answer is (D)