Which type of insect development involves three stages including egg, larva, and adult?

The correct answer is complete metamorphosis. This type of insect development consists of four distinct stages: egg, larva, pupa, and adult. In this process, the larva often looks very different from the adult, and there is a pupal stage that allows the insect to undergo significant transformation.

The other types of development listed do not accurately match the description provided in the question. Incomplete metamorphosis, for example, involves three stages: egg, nymph, and adult, where the nymph resembles a smaller version of the adult and grows through several molts. Gradual metamorphosis is generally a term used interchangeably with incomplete metamorphosis. Direct development involves no larval stage at all, as the young hatch from eggs and look like miniature adults, directly progressing to the adult stage without undergoing any significant transformation.