Fact 1: An egg requires warmth to survive.

Fact 2: Egg laying mammals are called monotremes.

Given the two facts above, answer the question "Monotremes require what for incubation?" with the following options: 
- nutrients
 - warmth
 - hormones
 - energy
 - Energy.
 - sunlight
 - heat
 - seeds


 

  warmth       