The correct answer is B. Playful
Explanation
In literature, the word mood is used to refer to an emotion that one the author transmits to the reader regarding something specific. According to the above, it can be inferred that the attitude of the character who is speaking in the extract is playful because it refers to a specific situation of the construction of a wall saying "Before I built a wall I’d ask to know What I was walling in or walling out" in a humorous and friendly way. According to the above, the correct answer is B. Playful