Collector Carl displays his beer can collection at the local swap meet. Mary sees the collection and is interested in buying it. Carl says he will sell the collection for $1,500. Mary says she really likes the collection but is only willing to pay $1,000. Which of the following is correct?a. Mary's offer is an option contract and she cannot revoke the offer.b. Mary's counteroffer terminates Carl's offer of $1,500.c. Neither offer is valid. Who would ever pay $1,000 or $1,500 for a beer can collection?d. If Carl rejects Mary's counteroffer, she can still accept Carl's offer of $1,500.