John Has Always Avoided Situations That Required Him to Be

John has always avoided situations that required him to be in contact with strangers. He never gave speeches in high school or college and never attended assemblies where people came together for a particular cause. His employment choices have been poor but allowed him to work independently. John has the knowledge and educational background to work for a major computer company, but he does not know how to overcome his fear of strangers. What diagnosis would a professional more than likely give John?

A) Paranoia
B) Anti-social behavior
C) Schizophrenia
D) Social anxiety disorder