Karen Has Agreed to Buy Sara's Car, but the Two

Karen has agreed to buy Sara's car, but the two have not agreed on the price. When there is no agreement as to price in a contract for a sale of goods, what effect does it have on the contract?

A) The price is whatever the seller decides.
B) The price is a reasonable price at the time of making the contract.
C) The price is a reasonable price at the time of delivery.
D) There is no contract, because the agreement is not definite and certain enough.