Which of the following would generally be considered a valid and enforceable offer?

a. An oral communication that a person will be agree to sell concert tickets for $50.

b. A car offered to the public by an auctioneer;

c. A newspaper advertisement for Macys

d. A nonbinding letter of intent to purchase real estate with a provision stating that the parties will formalize the terms of the deal in a written agreement with additional terms and provisions