Fact 1: Active immunity results when an immune response to a pathogen produces memory cells.

Fact 2: People with weaker immune systems are more likely to get sick from contaminated foods.

Given the two facts above, answer the question "What helps keep people from getting sick?" with the following options: 
- virus
 - sweating
 - bacteria
 - sensory neurons
 - Exfoliation
 - layers of fat
 - trees
 - Memory cells


 

        Memory cells 