Adler's concept of birth order was based on

A) his own experience.
B) ideas he learned from Freud.
C) what he learned from Jung.
D) his belief in the importance of biological factors in personality.

Adler's concept of birth order was mainly based on his own experience and observation of his own siblings. He also studied the birth order of his patients and friends, which influenced his theory. While Freud and Jung were influential in Adler's early career, his concept of birth order was largely his own contribution to personality theory, not directly influenced by either of them. Additionally, Adler emphasized environmental factors rather than biological factors in shaping personality.