The correct options are
A The quenching of a reaction can be made by cooling the reaction mixture.
B The quenching of a reaction can be made by diluting the reaction mixture.
C The reaction is supposed to be completed if it is kept for long time or strongly heated.
The quenching of a reaction can be made by cooling as well as diluting the reaction mixture. The reaction is supposed to be completed if it is kept for a long time or strongly heated. Quenching a reaction is used to deactivate any unreacted reagents. It is also done by adding an antisolvent to induce precipitation, and collecting or removing the solids.