Take a look at the passage again:
As waves of boring information rolled from Professor Clark's mouth. Kris
grabbed his mental surfboard and spent the rest of the hour riding fantasy
waves.
You chose to connect the subordinate clause to the main clause that follows, like this:
As waves of boring information rolled from Professor Clark's
mouth Kris grabbed his mental surfboard
and spent the rest of the hour riding fantasy waves.
Unfortunately, connecting these two parts requires specific punctuation. Review the rules.
Go back to the sentence to try again.