loss of nutrients in the forest soil lower air humidity in the forest changes to amount of light competition for survival
I gave my students this multiple choice question: Which environmental stimulus causes leaves on certain trees to change color in autumn?

Only one answer is correct among these 4 choices:
- loss of nutrients in the forest soil
- lower air humidity in the forest
- changes to amount of light
- competition for survival

Could you tell me which one is correct?

changes to amount of light