chicken eggs hatching paint fading to a lighter color apples ripening on the tree boulders weathering into gravel
I gave my students this multiple choice question: Which investigation would require the longest period of observation?

Only one answer is correct among these 4 choices:
- chicken eggs hatching
- paint fading to a lighter color
- apples ripening on the tree
- boulders weathering into gravel

Could you tell me which one is correct?

boulders weathering into gravel