Which of the Following Is an Example of a Quasi-Contract

Which of the following is an example of a quasi-contract?

A) Ann agreed to buy her colleague's house for $1 million and to take title on the subsequent Sunday.
B) A pizza delivery boy mistakenly leaves the neighbor's pizza on Ruby's fence and her son eats the pizza. The pizza boy asks Ruby to pay the bill.
C) A regular customer asks for a hamburger and is asked to pay $50 for it, though it is not listed on the menu.
D) Tom buys a cycle from his friend for $50 which Tom's father pays for.
E) Cindy offers to buy Nile's bat for $10 and he agrees to it in writing with both their signatures on paper.