Collector Charles displays his special can collection at the local swap meet. Madge sees the collection and is interested in buying it. Charles says he will sell the collection for $1,500. Madge says she really likes the collection but is only willing to pay $1,000. Which of the following is correct?

a. Madge's counteroffer terminates Charles's offer of $1,500.

b. If Charles rejects Madge's counteroffer, she can still accept Charles's offer of $1,500.

c. Neither offer is valid. Who would ever pay $1,000 or $1,500 for a special can collection?

d. Madge's offer is an option contract and she cannot revoke the offer.