You already have the right answer on your image. If you look at the pyramid, the ones on the higher part feed on the population below. So if the snake population will decrease, it would mean that less will feed on the rabbit population. This means there will be an increase in the rabbit population.
Now hawks are above the snake population, which would indicate that they feed on the snakes. If they have less food, which means that their population will decrease.
So the answer would be D. The population of hawks will decrease.. The population of rabbits will increase.
