Fact 1: Viruses cause many human diseases.

Fact 2: Some smallpox viruses are maintained in laboratories.

Given the two facts above, answer the question "What can smallpox cause?" with the following options: 
- contamination
 - harmful substances
 - vaccines
 - photosynthesis
 - extinction
 - cellular respiration
 - Destroy crops
 - human disease


 

        human disease 