"A cathedral is like a book; one must learn how to read it^ is an example of ... A. an idiom.

B. verbal irony.

C. a metaphor.

D. an analogy.

I would say an it's letter A idiom

The rhetorical appeal that relies solely on logic and reasoning is LOGOS. Logos represents the logic behind your arguments, and it is there so that you could persuade the audience using logical arguments and supportive evidence. So we can also conclude that it is a persuasive technique .