Adler's thinking and theory have been criticized as

A) inconsistent and unsystematic, with many gaps and unanswered questions.
B) rigid and exclusive, requiring total allegiance or complete rejection.
C) too complicated for any but specialists to understand.
D) so close to Freud that no significant differences are apparent.

Adler's thinking and theory have often been criticized for being inconsistent and lacking a systematic approach. Many gaps and unanswered questions remain in his work, which can make it difficult for those without specialized knowledge to understand. However, his theories do have some significant differences from Freud, as he emphasized the importance of social factors in shaping personality, rather than just unconscious drives.