Final answer:
David Elkind is the theorist who proposed that adolescent egocentrism is characterized by "the imaginary audience" and the "personal fable".
Step-by-step explanation:
The theorist who suggested that adolescent egocentrism is characterized by “the imaginary audience” and the “personal fable” is d) David Elkind. These concepts relate to the way adolescents tend to believe that their own experiences are unique and that they are constantly being observed by others. This is different than Jean Piaget’s concept of egocentrism in children, which is the inability to take the perspective of others. Erik Erikson, another influential theorist, focused on the psychosocial development and believed in the continuous development of personality across one's lifespan. However, it is David Elkind who is best known for these particular terms related to adolescent development.