* Autotrophs are organisms that can produce their own food through processes like photosynthesis (plants).

* Animals are heterotrophs, meaning they obtain their food by consuming other organisms.

Let's look at the other options:

* A. They are multicellular: Animals are indeed composed of multiple cells.

* B. Heterotrophic: As explained above, animals get their energy by eating other organisms.

* D. They lack cell walls: Unlike plants, animals do not have rigid cell walls.

* E. Most can actively move: This is generally true, although some animals like sponges and corals have limited movement.

Therefore, the correct answer is C.