A 62- year- old veteran underwent lung transplantation for idiopathic pulmonary fibrosis 6 months ago. His postoperative course has been complicated by a prolonged stay in the intensive care unit, renal insufficiency dependent on dialysis, atrial fibrillation, pneumonia, and severe deconditioning. He has difficulty working on his strengthening with physical therapy b/c he becomes anxious and worries about his perceived shortness of breath. He frequently asks to avoid or postpone these sessions and has been described as noncooperative with his treatment. This behavior, in turn, impedes his recovery. On evaluation by psychiatry, the pt denies depressed mood, reports enjoying visits from his family and watching the news, and is hopeful about his recovery. What is the likely diagnosis?

A. Adjustment disorder.
B. Generalized anxiety disorder.
C. Posttraumatic stress disorder.
D. Psychological factors affecting other medical condition.