Pineapples, unlike most other fruit, contain an enzyme called bromelain, that breaks up the gelatin into it's amino acid building blocks. [Enzymes are biomolecules that catalyze chemical reactions; most of them are proteins themselves.] Due to the bromelain, your jello doesn't become (or stay) solid.
It is the observed process in change.
All plants and animals are made of cells
Sorry If I'm wrong, but I'm pretty sure it's D.
