Question : What is NOT the cause of chronic respiratory disease?

Choose the letter A, B, C or D to answer these following questions

Chronic respiratory diseases (CRDs) are diseases of the airways and other structures of the lung. Some of the most common are chronic obstructive pulmonary disease (COPD), asthma, occupational lung diseases and pulmonary hypertension. In addition to tobacco smoke, other risk factors include air pollution, occupational chemicals and dusts, and frequent lower respiratory infections during childhood. CRDs are not curable, however, various forms of treatment that help dilate major air passages and improve shortness of breath can help control symptoms and increase the quality of life for people with the disease. The WHO Global Alliance against CRDs (GARD) has a vision of a world in which all people breathe freely, and focuses in particular on the needs of people with CRDs in low-income and middle-income countries.