The best answer is D
Pneumonia is an infection caused by fungi, bacteria and viruses. It is not caused by radiation.
Pneumonia causes inflammation of the air sacs called alveoli, in the lungs. Once inflamed, the alveoli fill with fluid and/or pus making the process of breathing difficult.
bacterial pneumonia is caused by a bacteria called Streptococcus pneumonia.
A type of fungi called mycoplasma causes mycoplasma pneumonia
The flu virus has been implicated in also causing viral pneumonia, usually in children.