A 60-year old man is diagnosed to be suffering from Legionnaires' disease after he returns home from attending a convention.He could have acquired it:

• A. From a chronic carrier in the convention center
• B. From a person suffering from the infection while travelling in the aeroplane
• C. By sharing an infected towel with a fellow delegate at the convention
• D. From inhalation of the aerosol in the airconditioned room at convention center