Take a look at the item again:
With the huge number of confusing rules colliding in her
head, (A)
Cindy took the quiz on fragments
(B) and
hoped, (C)
that she would remember enough of the material to pass.
You wanted to do this:
With the huge number of confusing rules colliding in her
head. Cindy took the quiz on fragments and
hoped, that she would remember enough of the material to pass.
The comma after head is incorrect. Substituting a period for the comma would make the opening phrase a fragment.
You might want to review the rules.
Go back to the sentence to try again.