Which of the following is an example of a bilateral contract? a) Eloise tells Griffin that she will pay Griffin $20 if he washes her car. Griffin then washes car. b) Eloise writes Griffin a letter in which she promises that if Griffin will wash her car, she pay him $20. Griffin then washes her car. c) Eloise and Griffin both sign a document which says, "Eloise agrees to pay Griffin $20 at Griffin agrees to wash Eloise's car in exchange for $20." d) Griffin washes Eloise's car without her knowledge and then requests payment of $20