The correct answer is - C: two, because they eat plants and insects.
Big portion of the monkeys are omnivorous, so when it comes to their occupation of the trophic levels they are occupying in a food chain, most of them occupy two of them. Because the monkeys eat both, plants and insects, as well as the occasional flesh (though not many species), they can be put in trophic level as plant eaters, and also as insect eaters.
While the plant eaters fall into the lower part of the trophic levels of the food chain, the insect eaters are higher into the hierarchy, as they are actually predators. This characteristic of performing the two different diets, gives the monkeys a different dimension in the food chain, and in fact, they can be put into a same category as the pigs and the bears.
