Occasionally a person will be unjustly enriched at the expense of another. No express contract exists. A contract can

[answerhappygod]

Occasionally a person will be unjustly enriched at the expense
of another. No express contract exists. A contract can
not be implied from the conduct of the parties, yet it would be
unjust for one individual to be enriched at the expense of the
other. A remedy created by law to correct such a situation is
called:
A. a unilateral contract
B. an executory contract.
C. a quasi-contract
D. an unenforceable contract.
Lucy orally agrees to clean Pig Pen's house for $110. When
she finishes, a dispute arises over whether or not Lucy was
supposed to have washed the windows and cleaned the oven. Pig
Pen tells Lucy that he will give her $90 instead of the full
amount. Lucy reluctantly agrees to accept the $90.
Which of the following is true?
A. The $110 is a liquidated debt.
B. The $110 is an unliquidated debt.
C. The parties have entered into a collateral contract.
D. All of the above.