Fact 1: Feathers help birds fly and provide insulation.

Fact 2: Straight feathers are dominant to curly feathers .

Given the two facts above, answer the question "a part of birds where what is dominant to curly helps them fly and provides insulation?" with the following options: 
- Animal fur
 - bioaerosols
 - fur and fat
 - Vanes
 - Epidermis
 - sweating
 - staying warm
 - straight


 

        straight 