Fact 1: Some viruses can cause cancer.

Fact 2: Cancer is an example of a mutation in cells.

Given the two facts above, answer the question "What can mutate cells?" with the following options: 
- Allergies
 - water
 - fruits
 - flow of electrons
 - vegetables
 - harmful substances
 - rays or beams
 - some viruses


 

        some viruses 