Dean Yim-Yu Wong of S.F.S.U.s School of Business hires the worlds most famous International Dance Troupe The End of the Alphabet Dancers, (BUS 320 Survivors Di Wang, Fiona Xie, David Yee, and Di Zhang) choreographed by illustrious B-Law Survivor Jackie Stanky Leg Chang, to teach her Business Law faculty the latest Global hip-hop dances. The End of the Alphabet Dancers quoted Dean Wong a price of $6,000 per faculty member for the dance instruction. After 20 minutes of lessons, the troupe discovered that the faculty has absolutely no rhythm and incredibly, they each have two left feet! To teach this overwhelmingly old and rhythmatically challenged group would take substantially more time and cost more money. The troupe say they will continue, but only if Dean Wong pays them $2,000 for each extra left foot. Dean Wong agrees. If Dean Wongs promise to pay an increased amount is enforceable it is because:

a. This is a valid settlement of a liquidated debt.

b. This is a preexisting duty.

c. This is a Uniform Commercial Code modification.

d. This is an unforeseen circumstance.

e. This is a novation.