they have scaly skin. they have slimy skin. their body temperature stays at a constant level. their body temperature changes with the environment.
I gave my students this multiple choice question: Reptiles become more active as the day gets warmer. This is because

Only one answer is correct among these 4 choices:
- they have scaly skin.
- they have slimy skin.
- their body temperature stays at a constant level.
- their body temperature changes with the environment.

Could you tell me which one is correct?

their body temperature changes with the environment.