Fact 1: Courtship is behavior that is intended to attract a mate.

Fact 2: For example, female birds secrete estrogen in response to the courtship of their male mates.

Given the two facts above, answer the question "What do birds secrete to attract a mate?" with the following options: 
- Energy.
 - Energy
 - fur and fat
 - seeds
 - oxygen
 - pollen
 - Estrogen
 - acetic acid


 

       Estrogen  