Final answer:
The author's reference to Mark Twain in the passage from 'The Unseen Values' shifts the tone of the last section by using a shared experience to create a sentimental tone.
Step-by-step explanation:
The author's reference to Mark Twain in the passage from 'The Unseen Values' shifts the tone of the last section by using a shared experience to create a sentimental tone. By mentioning Mark Twain listening to the complaints of an old riverboat pilot, the author is able to connect with the reader on a personal level and evoke emotions of nostalgia or fondness for the past. This shift in tone helps the author effectively convey the message that sometimes change is necessary, even if it is difficult or resisted.