L.5.2.C Use a comma to separate an introductory element from the rest of the sentence. Use a comma to set off appositives, the words yes and no (e.g., Yes, thank you.), to set off a tag question from the rest of the sentence (e.g., It's true, isn't it?), and to indicate direct address (e.g., Is that you, Steve?). Use punctuation to separate items in a series.