Concept:Germs that infect the respiratory system (e.g. those causing common cold, influenza, tuberculosis, COVID-19) are carried in the mucus and droplets that come out of an infected person's nose and mouth.
Solution:I. Mucus: nasal and throat mucus (catarrh, sputum) carries the germs; touching it or using an infected person's handkerchief spreads them. Correct.
II. Air pollution: smoke, dust and harmful gases irritate and damage the airways, but pollution is not a way germs are passed from one person to another. Not correct.
III. Coughs: coughing and sneezing spray germ-filled droplets into the air, and others breathe them in. Correct.
So germs are spread through I and III.
Key point: The paper printed the options I only, II only, II and III only, and I, II and III, and its key gives (C) II and III only. None of them is correct, because air pollution is not a carrier of germs. Option B has been replaced with the correct combination, I and III only.
Answer:Option B (I and III only)