Anna offers to sell her house to Daniel in consideration of $220,000. Daniel says he will pay $219,000. What is the status of this exchange of promises at this time?

a. This is a bilateral, valid contract because the difference of less than one-half of one percent is trivial and not material.

b. This is a unilateral contract that can only be accepted by performance.

c. This is an offer and a counteroffer that terminates Daniel's power of acceptance of the original offer.

d. This is an offer and a counteroffer that does not violate the mirror image rule of contracts because the UCC is applicable to real estate contracts. Daniel can still create a contract by accepting the original offer.