If water is called food, food is called tree, tree is called sky, and sky is…

In a renaming-substitution coding-decoding puzzle, the code only changes the LABELS used for real-world objects — the underlying real-world facts never change. To answer, first identify the real-world fact the question depends on, then trace the substitution chain to find the current label attached to that real object.

1. The given code chain is: water → food, food → tree, tree → sky, sky → wall (each arrow shows what the real object on the left is now called).

2. The real-world fact needed here is unaffected by the code: a fruit grows on a tree.

3. Trace the label for 'tree': the code states tree is called sky, so the real object tree is now labelled 'Sky'.

4. Therefore, in the terms used by this code, a fruit grows on 'Sky'.

Cross-check by tracing the other options back to their real-world referent: 'Water' is not reassigned by the code, so it still means water; 'Food' is the new label for the real object water (since water is called food); and 'Tree' is the new label for the real object food (since food is called tree). None of these three is the real object a fruit grows on, confirming 'Sky' is the only option that maps back to 'tree'.

Result: a fruit grows on 'Sky'.