Consideration may be:

Past:
- In contract law, past consideration refers to a promise made in return for a prior act or service that has already been performed.
- Generally, past consideration is not valid consideration because it lacks the necessary element of exchange.
- However, there are certain exceptions where past consideration can be recognized as valid, such as when there is a moral obligation or a promise to pay a debt that is already owed.

Present:
- Present consideration refers to the exchange of promises or acts that are made at the same time.
- It is the most common form of consideration in contract law, where both parties provide something of value to each other.
- For example, if person A promises to pay person B a certain amount of money in exchange for a service provided by person B, this would be considered present consideration.

Future:
- Future consideration refers to a promise or act that is made in exchange for a future act or event.
- It involves a promise to perform an obligation or provide something of value at a later date.
- For example, if person A promises to pay person B a certain amount of money in exchange for a service that will be provided by person B in the future, this would be considered future consideration.

All of the above:
- Consideration can exist in the past, present, or future.
- The key requirement for consideration is that it involves a bargained-for exchange between the parties involved in a contract.
- It can be something of value (money, goods, services) or a promise to do or not do something.
- The concept of consideration ensures that both parties have provided something of value and have entered into the contract willingly and knowingly.

Therefore, the correct answer is option 'D' - All of the above. Consideration can exist in the past, present, or future, depending on the circumstances of the contract.