Margo gave Bobby her class notes in biology for a whole year while they were dating. She told him at the time they were worth $$50$ and he agreed. When they broke up the next fall, she demanded $$50$ for the notes. Is she entitled to the money:

a$.$ Yes. They had a quasi$-$contract.

b$.$ No$.$ The notes were past consideration by the time she asked for the money.

c$.$ Yes. The notes were sufficient consideration to create a contract.

d$.$ Yes. Under the doctrine of promissory estoppel, she should be rewarded.