The correct answer is - D. secondary consumers.
As the snake is a predator, it falls into the category of the tertiary consumers, which means that it mostly feeds on the secondary consumers, in this case, the mice.
If the snakes are eliminated from the suggested food chain, than the main increase in numbers will be witnessed at the secondary consumers, the mice in this case, as they will lose one of their prime predators.
Since less mice will be eaten, as the owls will be their only predator, more mice will reproduce, thus their numbers will increase significantly.
