Mr WONG, a 73-year-old man, made a regular visit to his general practitioner and complained of gradual deterioration in exercise tolerance, as he could only manage to climb up one flight of stairs in the recent six months in contrast to three flights of stairs one year ago. He has been a chronic smoker for the past 50 years, with an average daily consumption of one pack of cigarettes. He has been having chronic productive cough and shortness of breath almost daily in the past six months.

a) What is his most likely clinical condition? (2 marks)

b) Name TWO classes of drugs with examples and their drug action to improve Mr WONG's breathing problem. Describe the benefits of their routes of administration. (10 marks)

c) Which combination therapy instead of monotherapy is currently approved for better management of such a condition? What is the rationale for such drug combination? (4 marks)

d) List ONE class of therapeutic drug with one example that can be added to relieve his chronic productive cough. State the mechanism of action for such a drug. (4 marks)