Take another look at the passage:

As he scrubbed the tile grout with a toothbrush and bleach. Nick vowed never again to let the bathroom get so filthy.

You chose to move the main clause to the front, like this:

Nick vowed never again to let the bathroom get so filthy, as he scrubbed the tile grout with a toothbrush and bleach.

Unfortunately, you do not use a comma to connect this subordinate clause to the end of the main clause. Review the rules.

Go back to the sentence to try again.

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