Review the item:
Frances searched the car trunk,
on the pantry shelves, and
the top of the refrigerator, but she could not
find the box of cornflakes that she did remember buying.
When you list grammatical items, you must use parallel structure. Here, the car trunk and the top are both noun phrases, but on the pantry shelves is a prepositional phrase, wrecking the parallelism.
To fix the error, change on the pantry shelves to the pantry shelves.