This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory, Subject name: Medicine
A 23-year-old man notices a gradual but progressive increase in breathing difficulty. He has a long history of back pain with prolonged morning stiffness. He has also had an episode of iritis in the past. On examination, there is reduced range of motion in the lumbar spine with forward flexion and pain on palpation of the sacroiliac joint and surrounding soft tissue. X-rays of the pelvis show erosions and sclerosis of the sacroiliac joint. Which of the following is the most likely pulmonary complication of this condition? 
Select and explain. 
A. fibro cavitary disease, B. airflow obstruction, C. bilateral lower lobe involvement, D. pleural effusions
A: fibro cavitary disease
Answer: A: fibro cavitary disease 
Explanation: Ankylosing spondylitis is characterized by bilateral upper lobe fibrosis, which may be complicated by fibro cavitary disease. The pulmonary involvement is rare and is usually very slowly progressive. The cavities can be colonized by Aspergillus.