On Monday, O'Shea tells Patterson that she will pay Patterson $1,000 if O-Shea's bill processing and office filing are completed by Friday. On Wednesday, when Patterson has finished more than half of the work, O'Shea says that she has changed his mind. Under the modern-day view, these parties had

a. an expired contract when O'Shea said that she changed her mind.
b. a bilateral contract when O'Shea offered to pay for the work.

c. a unilateral contract as soon as Patterson began to perform.

d. no contract.

c