I heard his car pulling out and couldn't answer. So I went back to fiddling my favorite tune, Cotton Eyed Joe. Tune up your fiddle and rosin your bow. A capital letter signals the start of a new sentence. A period, question mark, or exclamation point signals the end of the sentence.
Commas signal the breaks between three or more units in a series.
When two or more independent clauses are compounded, a comma comes before the conjunction. When a modifying phrase or clause comes before the independent clause in a sentence, a comma marks the end of the introductory phrase or clause. When an interruption enters a sentence, a comma or commas set it off from the rest of the sentence. Insert a comma or commas where they are necessary in the following sentences. Compare your work to the computer's responses.