The correct answer is - A. The population of predators could increase.
If in a particular food web a new prey animals are introduced, that will most likely result in the increase of the populations of the predators in that food web. The reason why the populations of the predators would increase is that there will be more pray to hunt, and more food means that the predators can increase in numbers and not suffer from food shortage.
Still, while this the most likely scenario, it has to be taken with a little bit of reserve, as it also depends on what kind of prey animal would be introduced in the food web, and what kind of predators are there in the food web. If lets say a prey animal that is large is introduced, like the buffalo, and the predators in that food web are small to medium sized predators like the genette, caracal, serval, honey badger, than there will be no increase in the predator populations as they will not be able to hunt the introduced pray animal.