Final answer:
All provided examples where Ed proposes to sell a pen for $1 are offers under contract law, including verbal, formal statements, and written notes, since they express willingness to contract on specific terms with the intention of being binding upon acceptance.
Step-by-step explanation:
Each example provided in the question, where Ed makes a statement about selling his pen for $1, is an illustration of an offer. An offer in contract law is a clear proposal to sell something, which, if accepted, forms the agreement needed for a contract.
Whether Ed says it out loud (A. Ed says "I'll sell you my pen for $1."), writes it in a formal statement (B. Ed says "I offer to sell you my pen for $1"), or sends a note , each of these actions constitutes an offer as they are expressions of willingness to enter into a contract on specific terms, made with the intention that it shall become binding as soon as it is accepted by the person to whom it is addressed.
Therefore, the correct answer to which one is an offer is D. All of the above.