Answer:
The correct answer is B.
Explanation:
The terms "pilot-house" and "paddle-boxes" affect the passage in the way that they emphasize Twain's knowledge of the parts of a ship and stress the authenticity of the descriptions.
In the text says "a fanciful pilot-house" and it is between commas in order show special emphasis to the "pilot-house" which is one of the parts of the shhip. The same happens with the phrase "the paddle-boxes are gorgeous with a picture" the author makes special emphasis in another part of the ship.