Q: 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
Let's think step by step below.

User
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.
Thus, the answer is (D).
Assistant