to keep the eggs inside the nest to keep the eggs warm to protect the eggs from the wind to protect the eggs from the rain
I gave my students this multiple choice question: Most birds sit on their eggs until they hatch. Which of these is the most important reason why birds sit on their eggs?

Only one answer is correct among these 4 choices:
- to keep the eggs inside the nest
- to keep the eggs warm
- to protect the eggs from the wind
- to protect the eggs from the rain

Could you tell me which one is correct?

to keep the eggs warm