Fact 1: Populations of viruses do not grow through cell division because they are not cells.

Fact 2: Viruses are the cause of many diseases.

Given the two facts above, answer the question "What aren't diseases caused by?" with the following options: 
- ovaries
 - bacteria
 - A drug.
 - humans
 - cells
 - infection
 - virus
 - cats


 

     cells    