The word metamorphosis refers to a profound change in form, nature, or structure. It is most commonly used in biology to describe the process of an animal physically developing after birth or hatching.
Change (D): This is the closest synonym. Whether it is a caterpillar becoming a butterfly or a person undergoing a major life transformation, the core of the word is "change."
Consistency (A), Stagnation (B), and Stability (C): These all imply staying the same, lack of movement, or staying fixed in one state. They are actually antonyms (opposites) of metamorphosis.