Supervening impossibility, also known as subsequent impossibility, refers to a situation where it becomes impossible to perform a contract after its formation. This concept is recognized and addressed in contract law to determine the rights and obligations of the parties involved.

Below are the explanations of the given options:

a) Supervening impossibility: This is the correct answer. It refers to the impossibility that arises after the formation of a contract.

b) Subsequent impossibility: This is another term used to describe the same concept as supervening impossibility. It refers to the situation where impossibility arises after the contract is formed.

c) Both of above: This option is correct because both supervening impossibility and subsequent impossibility refer to the same concept.

d) None of these: This option is incorrect as both a) and b) are correct.

Now, let's discuss the concept of supervening impossibility in more detail:

1. Definition: Supervening impossibility occurs when an unforeseen event or circumstance arises after the formation of a contract, making it impossible for one or both parties to fulfill their obligations.

2. Doctrine of Frustration: Supervening impossibility is often addressed under the doctrine of frustration. This doctrine recognizes that certain events or circumstances may render the performance of a contract impossible, impracticable, or radically different from what was originally contemplated.

3. Elements of Frustration: To establish frustration, certain elements must be present:

a) Unforeseen event: The event must be unforeseen and beyond the control of the parties. It should not have been anticipated or provided for in the contract.

b) Impossibility: The event must render the performance of the contract impossible. It should not merely make performance more difficult or expensive.

c) No fault of the parties: The event should not be due to the fault or negligence of either party. It should be an external event that neither party could have reasonably foreseen or prevented.

4. Consequences of Frustration: When a contract is frustrated due to supervening impossibility, it is generally discharged, and the parties are relieved from further performance. They are also relieved from any liability for non-performance.

5. Allocation of Losses: In cases of frustration, the losses caused by the supervening impossibility are borne by the parties as per the principle of restitutio in integrum. This means that the parties are restored to their pre-contractual position as far as possible.

In conclusion, supervening impossibility refers to the situation where it becomes impossible to perform a contract after its formation. It is recognized under the doctrine of frustration and leads to the discharge of the contract. Both the terms "supervening impossibility" and "subsequent impossibility" refer to the same concept.