Fact 1: Viruses cannot reproduce by themselves.

Fact 2: Viruses Viruses are the smallest agents of disease.

Given the two facts above, answer the question "the smallest agents of what cannot reproduce by themselves?" with the following options: 
- Pesticides
 - bacteria
 - Allergies
 - fungi
 - animals
 - dangerous
 - ferns
 - disease


 

        disease 