Take a look at the passage again:
Ralph spent all of his savings on a diamond ring
to give to his girlfriend Melanie. A greedy young woman who had a
box full of expensive trinkets from ex-boyfriends. Melanie was always looking
for the man with the fattest wallet.
You chose the first part, Ralph spent all of his savings on a diamond ring to give to his girlfriend Melanie. This part has a main clause: Ralph is the subject; spent is the verb. A fragment will not have a main clause.
Go back to the passage to try again.