Which of the Following Is the Best Description of Discharge

Which of the following is the best description of discharge by waiver?

A) One party leads the other to reasonably believe that strict performance will not be insisted upon.
B) A new agreement is substituted for the old by the parties.
C) Both parties abandon their original agreement while it is still executory.
D) A party who has already performed their obligation agrees to relieve the other party from performing their obligation in return for their doing something different.