Fact 1: Infection can cause bodily tissues to swell.

Fact 2: Doctors call such tissue swelling edema.

Given the two facts above, answer the question "What causes edema?" with the following options: 
- An infection
 - amoebae
 - heating liquids
 - An antibiotic
 - smoking
 - Vitamins
 - prolactin release
 - Food poisoning


 

 An infection        