Pneumonia may be caused by an infection or injury of the lungs.
Infections of the lungs can be caused by bacteria, viruses or fungi.
Pneumonia may be caused by viruses or injury .
Pneumonia may be caused by viruses or 
(A) bacteria
(B) a hazard
(C) cold weather
(D) humidity
(E) mildew
(F) PDAs
(G) injury
(H) methane