Answer: A. a made-up name
Explanation: Look at the context clues. The paragraph says, "Carolyn Keene is a pseudonym created by the series' father, Ed Stratemeyer, and it is shared by an unknown number of ghost writers." This tells the reader that Carolyn Keene is an example of a pseudonym, that a pseudonym is created, and that a pseudonym can be shared by ghost writers. A pseudonym is "a made-up name."