The right answer is letter C: When you have finished, clean up your area. This sentence starting with "when" as a relative pronoun supposes a dependent clause will be separated from an independent one by a comma "clean up your area".
Option A follows a standard structure where the dependent clause follows the independent one; option B shows "cleaning up" as a detail for "finishing" as the subject of the sentence; and option D uses "cleaned" as an adjective after a modal verb "should".
