If a mouse eats grass, a snake eats the mouse, and an owl eats the snake, the snake is considered the
a. producer.
b. secondary consumer.
c. primary consumer.
d. tertiary consumer.

Grass is the producer, mouse is the primary consumer, snake is the secondary consumer and owl is the tertiary consumer.

Mouse ate the grass, so he's primary, if something eats it, it's secondary. Snakes are usually depicted as tertiary consumers due to the addition of insects in food chain representations, and that can be confusing when looking at "insectless" food chains (like this one).