Marcy tells jessica that she will buy jessica a new dress if she reads a book by friday night. jessica begins reading and has only two chapters left to finish when marcy tells jessica that she has changed her mind and will not buy the dress. under the modern approach to contracts, marcy and jessica
a. formed a unilateral contract as soon as jessica began reading.
b. formed a bilateral contract as soon as jessica began reading.
c. have not formed a contract, and marcy owes jessica nothing.
d. have no contract until jessica finishes reading.