We must go now, ________.
Add a correct question tag.

The correct answer is Option B (mustn't we?).

Key Points:
• This question evaluates the rules for forming Question Tags.
• Option 2 is correct. The rule for question tags is: if the main sentence is affirmative (positive), the question tag must be negative. The auxiliary verb used in the tag must match the auxiliary verb in the main sentence. Here, the sentence is 'We must go now' (positive). The auxiliary verb is 'must'. Therefore, the tag takes the negative contraction of 'must', which is 'mustn't', followed by the subject pronoun 'we'. Result: 'mustn't we?'.
• 'are we' uses the wrong auxiliary verb. 'don't we' would be used if the sentence lacked a modal auxiliary (e.g., 'We go now'). 'must we' is a positive tag, which is incorrect for a positive statement.
• Ensure the tag's polarity (positive/negative) is opposite to the main clause, and strictly use the existing auxiliary verb.
• Key Takeaway: Remember: Positive statement -> Negative tag. Use the same auxiliary verb. (must -> mustn't).