Take a look at the sentence again:
We searched the car trunk, __________, and the top of the refrigerator,
but we could not find the box of cornflakes that we remember buying.
The blank requires a noun phrase. You chose looked on the pantry shelves, which contains an unnecessary verb, looked, and an unnecessary preposition, on. Before you continue, review the rules for parallel structure.
Go back to the sentence to try again.