You are presented with the question "What helps keep people from getting sick?" and the following answer choices: 
- virus
 - sweating
 - bacteria
 - sensory neurons
 - Exfoliation
 - layers of fat
 - trees
 - Memory cells

Now knowing that active immunity results when an immune response to a pathogen produces memory cells and people with weaker immune systems are more likely to get sick from contaminated foods, choose the best answer.


 

        Memory cells 