When is a person's duty to perform discharged on grounds of impossibility?

A) When a substitute is available
B) When there is a delay in the delivery of goods
C) In the presence of supervening illegality
D) A promisee's dissatisfaction with the performance

Supervening Illegality

A situation where a law change after an agreement is made renders the performance of the contract illegal.

Impossibility

A concept in contract law where unanticipated events make the fulfillment of a contract's terms unfeasible or unable to be completed.

Substitute

An alternative or replacement for something else, particularly in the context of products, goods, or services.