The correct answer is B.

Explanation: The sentence "Walk the dog right now, ____________" is an imperative sentence where the speaker is giving a command or request. To turn it into a polite request or suggestion, the appropriate tag question is:

- B. will you? This is the correct tag question to use with an imperative sentence. It politely asks for confirmation or agreement to the request.

Other options:
- A. walkn't you?: This is not a correct or standard tag question form.
- C. shall you?: This is not commonly used as a tag question for imperatives.
- D. would you?: This is a valid tag question but is more commonly used with requests or suggestions rather than direct commands.

Thus, "will you?" best completes the sentence.