Explanation:

- Sale:

- A sale is a transfer of ownership immediately upon the agreement.

- The seller and buyer exchange goods and consideration at the moment of agreement.

- Agreement to Sale:

- An agreement to sell refers to a future contract.

- The ownership will transfer at a later date upon fulfillment of specified conditions.

- This is the case for contingent goods, where the sale depends on certain conditions being met.

- Contingent Sale:

- This term is not commonly used in formal contract law.

- It could be misinterpreted as any sale dependent on conditions.

- Contingent Agreement:

- This term suggests an agreement dependent on uncertain events.

- It's not a standard term like "agreement to sale."