Fact 1: Viruses cannot reproduce by themselves.

Fact 2: Viruses are germs that cause people to get sick.

Given the two facts above, answer the question "germs that cause people to get sick cannot reproduce by what?" with the following options: 
- anemia
 - dry conditions
 - harm them
 - contamination
 - burning coal
 - Smoking
 - heat or cold
 - themselves


 

        themselves 