Take a look at the passage again:
Chewing the dry, tough, whole-grain bread bought from the health food store.
Lorena tried to enjoy her lunch. Fantasizing
about a juicy cheeseburger on a soft white bun didn't improve the taste
of the soy product sandwiched between leaves of organic lettuce.
You chose the second part, Lorena tried to enjoy her lunch. This part has a main clause: Lorena is the subject; tried is the verb. A fragment will not have a main clause.
Go back to the passage to try again.