A, autotrophs belong to producers, located in the first trophic level of the food chain, and A is correct;

B, herbivores belong to primary consumers, located in the second nutritional level of the food chain, B error;

C, carnivores belong to at least the second-class consumers, at least in the third trophic level of the food chain, C is wrong;

D parasites belong to consumers and cannot be located at the first nutritional level of the food chain. D is wrong.

So choose: a.