Who can file a suit under Section 91 of Civil Procedure Code for public nuisance?

Ordinarily an amendment of pleading in a suit may be carried out by the contesting parties under Order VI Rule 17 of the Code of Civil Procedure 1908.The court may allow the amendment:
1. In case the changes carried out in the pleading do not change the relief claimed for.
2. At any stage of the suit.
3. Without imposing costs.
4. Of an application filed for interim relief.
Select the correct answer:

Under Order 8 Rule 6 Code of Civil Procedure set-off may be permitted if-

On rejection of a suit under Order VII, Rule 11 of Code of Civil Procedure, a fresh suit on the same cause of action under Order VII, Rule 13 of Code of Civil Procedure

Mesne profits as defined under section 2(12) Code of Civil Procedure means those profits which the person in wrongful possession of