Fact 1: Some parasites live on the surface of their host.

Fact 2: Fleas and ticks are parasites.

Given the two facts above, answer the question "what sometimes lives on the surface of their host?" with the following options: 
- lungs
 - an organism's body
 - human
 - barnacles
 - fleas and ticks
 - density
 - sensory neurons
 - bacteria


 

     fleas and ticks    