Answer the following question: You are presented with the quiz "An allergy can be caused by" But you don't know the answer, so you turn to your teacher to ask for hints. He says 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". So, what's the best answer to the question?

Available choices:
(I). antigens;
(II). Pesticides;
(III). cold weather;
(IV). fever;
(V). viruses;
(VI). food;
(VII). Smoking;
(VIII). germs;
Answer:
(I).