Explanation:

- Offer: An offer is a clear proposal to enter into an agreement. It is an essential part of contract formation but not the agreement itself.

- Proposal: This is another term for an offer. It represents the willingness to enter a contract but isn’t the binding agreement.

- Consideration: This refers to something of value exchanged between parties, a requirement for a contract but not a contract itself.

- Contract: A contract is a legally binding agreement creating obligations between parties. It involves elements like offer, acceptance, and consideration.

- Correct Answer: Option 4 - Contract