Excavation Inc

Excavation Inc. begins digging a foundation for Financial Investment Company under a contract for a certain price. After six months, Excavation demands a higher price because of extraordinary difficulties that were totally unforeseen at the time the contract was formed. An agreement to pay the higher price is

A) enforceable as the consideration is past.
B) enforceable due to unforeseen difficulties.
C) unenforceable as an illusory promise.
D) unenforceable due to the preexisting duty rule.