Final answer:
In Atticus's choice of book, 'The Gray Ghost,' the use of the book as a representation of Boo Radley's life is best described as a metaphor, highlighting the deeper connections and revelations of Boo's true nature by the story's end.
Step-by-step explanation:
The book The Gray Ghost that Atticus chooses to read is a metaphor for the life of Boo Radley. A metaphor is a figure of speech in which a word or phrase is applied to an object or action to which it is not literally applicable. In this case, Boo Radley is likened to the character in The Gray Ghost, symbolizing how Boo is misunderstood and misjudged by the society, but in the end, is revealed to be good-hearted, much like the character in the book Atticus reads.
An analogy is a comparison between two things, typically for the purpose of explanation or clarification. A simile is a figure of speech involving the comparison of one thing with another thing of a different kind, used to make a description more emphatic or vivid, often marked by the use of the words "like" or "as". Personification assigns human traits to non-human objects or abstract ideas. In this context, metaphor fits best as it represents a direct correlation between Boo and the content of the book without using 'like' or 'as' for comparison, and without giving human character to non-human objects.