Solution:Major Indoor Pollutants and Their Sources
A. Nitrogen oxides - Fuel combustion (IV): Produced mainly from gas stoves, kerosene heaters, and other combustion appliances used indoors.
B. Lead - Remodelling of painted surfaces (III): Commonly released from old leadbased paints during renovation or repair activities.
C. Radon - Soil under buildings, construction materials (1): A radioactive gas naturally emitted from soil and rocks, seeping into buildings through cracks.
D. Aldehydes - Furnishings (II): Found in pressed wood furniture, carpets, and adhesives, releasing formaldehyde vapors indoors.
Correct Answer: 2. A-IV, B-III, C-I, D-II.