Final answer:
Mark Twain uses the idiom "in a twinkling" to describe the rapid transformation of a sleepy town becoming lively, which conveys the quickness and spontaneity of the change, making option C the correct answer.
Step-by-step explanation:
Within the vibrant excerpt from Mark Twain's Life on the Mississippi, the phrase "and all in a twinkling the dead town is alive and moving" showcases Twain's use of an idiom. An idiom is a phrase or expression whose meaning cannot be understood from the literal interpretation of the words; it is a form of speech that is figurative. The correct answer to how Twain uses an idiom in this excerpt is C. The idiom emphasizes the swiftness with which the town transitions from silence to bustling activity. It conveys the notion that the town comes to life almost instantaneously, illustrating the transition with a sense of rapid, magical transformation.