Question

Which of the following needs a comma? Clean up your area when you have finished. Finishing includes cleaning up your work area. When you have finished clean up your area. Your area should be cleaned after you finish.

Answer 1

When you have finished, clean up your area.

Answer 2

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".