Answer the following question given this paragraph: 

Did you ever hear of hay fever? It’s not really a fever at all. It’s an allergy to plant pollens. People with this type of allergy have symptoms such as watery eyes, sneezing, and a runny nose. A common cause of hay fever is the pollen of ragweed. Many people are also allergic to poison ivy ( Figure below ). Skin contact with poison ivy leads to an itchy rash in people who are allergic to the plant.


Q: Hay fever is actually an allergy to what substance, vital to plant reproduction?

 Choices:

- nitrogen

- fungi

- grass

- pollen

A:
pollen
