A 45- year- old man presents to his primary care doctor, complaining of chronic chest pain for the past year. He has seen multiple specialists, who tell him the pain is from uncomplicated acid reflux; however, he thinks he must have serious heart disease. He continues to worry about his heart despite reassurance from multiple cardiologists; he acknowledges that it is possible the cardiologists are correct. He denies hallucinations, and there is no evidence of delusional content. His concern about his heart has prevented him from vacationing with his family. He denies feeling depressed or anxious or having any problems with sleep or appetitie, and he continues to enjoy hobbies at home. What is the likely diagnosis?

A. Generalized anxiety disorder.
B. Illness anxiety disorder.
C. Major depressive disorder.
D. Panic disorder.