Choose the correct sentence/s with correct question-tag.
(a) One can't be faithful to all, can one?
(b) We have lunch at 1 pm, do we?
(c) They have a big factory, haven't they?
(d) She is in her sixties, doesn't she?
Answer Options :

The correct answer is Option D (Only (a) and (c)).

Key Points:
• (a) 'One can't be faithful to all, can one?': The statement is negative ('can't') with pronoun 'one', so the positive tag 'can one?' is completely correct.
• (b) 'We have lunch at 1 pm, do we?': The statement is positive, so the tag must be negative ('don't we?'). 'do we?' is incorrect.
• (c) 'They have a big factory, haven't they?': In British English, when 'have' denotes possession as a main verb, 'haven't they?' is an accepted question tag.
• (d) 'She is in her sixties, doesn't she?': The verb is 'is', so the tag must be 'isn't she?'. 'doesn't she?' is incorrect.
• Thus, (a) and (c) are correct.
• Key Takeaway: Negative statements take positive tags ('can't' → 'can one?'); 'have' for possession can take 'haven't they?'.