Andrew Agrees to Paint Betty's House for $500

Andrew agrees to paint Betty's house for $500.Two days after he starts the job,he decides that $500 isn't enough money.He refuses to finish the job unless Betty agrees to pay him $100 more.What law applies to this fact situation?

A) The acceptance of additional money to settle a disputed claim is supported by consideration.
B) A past obligation is sufficient consideration for a new promise.
C) Andrew gives no additional consideration in return for modification of a preexisting contract.
D) Betty has made a promise in exchange for a forbearance.