Mona hires Ernie's Excavation to dig a hole for $5000. When Ernie begins digging, he discovers excessive rock in the ground thatnobody was aware of. He tells Mona it will cost an extra $2,500 for the excavation work and she agrees, but later refuses to pay any more than the original $5,000 contract price. If Ernie sues

a.

Ernie wins because Mona was not acting in good faith.

b.

Mona will win because this was extortion and illegal.

c.

Mona wins because Ernie had a preexisting duty to dig the hole.

d.

Ernie will winbecause the contract modification was due to unforeseen difficulties.