Question $19($Mandatory$)(2$ points$)$

Under a contract with Townhouse Villas, Inc., a residential development, William begins grading a terraced hillside. Halfway through the project, William asks for $$5,000$ over the contract price, claiming an increase in the "cost of doing business." Townhouse Villas agrees. This agreement to pay more is

$$ a$)$ unenforceable because William's performance was a preexisting duty.

b$)$ unenforceable because William's request modified the contract.

c$)$ enforceable.

d$)$ unenforceable because Townhouse Villa's promise was illusory.