19. Pneumonia is

A. a bacterial infection.

B. a viral infection.

C. not treatable.

D. an upper respiratory infection.

A. a bacterial infection.

A bacterial infection

Explanation:

Pneumonia is an infection in one or both lungs. Bacteria, viruses, and fungi cause it. The infection causes inflammation in the air sacs in your lungs, which are called alveoli. The alveoli fill with fluid or pus, making it difficult to breathe.