You are presented with the question "An allergy can be caused by" and the following answer choices: 
- antigens
 - Pesticides
 - cold weather
 - fever
 - viruses
 - food
 - Smoking
 - germs

Now knowing that antigens are molecules that the immune system recognizes as foreign to the body and an allergy is a reaction to a substance the body recognizes as foreign, choose the best answer.


 

 antigens        