Final answer:
Metamorphosis is the phase in many animals' life cycles where a rapid transition from the immature to the adult form occurs, and it includes both complete and incomplete metamorphosis.
Step-by-step explanation:
The correct answer is A) Metamorphosis. The phase in the life cycle of many animals during which a rapid change from the immature form of the organism to the adult form takes place is called metamorphosis. This significant developmental transition can involve both complete metamorphosis and incomplete metamorphosis. In complete metamorphosis, exemplified by butterflies, the organism goes through distinct stages, including larva, pupa, and adult, which look completely different from one another and often have different habitats and behaviors. Insects such as grasshoppers undergo incomplete metamorphosis, where the immature forms (nymphs) resemble wingless adults and gradually develop adult features through successive molts.