Which of the following contracts would be valid?

a.Elise and her18year old son sign a contract where Elise promises to give her son a car of his choice if he doesn't drink until he is21.

b.A contractor discovers a pipe in the way when he is building his client's house and it will cost him an additional$10,000to move it.He then gets his client to sign a new contract to cover the additional$10,000.

c.Al sells an ugly painting at his garage sale to Brian for$5.Brian then tells him that he just bought a Van Gogh worth$60,000.Al wants to get out of the deal,can he?

d.Sue sees a telethon on the television and feels sorry for the people who need help.She calls in and pledges$100.

e.A company sends Wyatt a DVD in the mail and states that if he decides to keep the DVD he owes them$15.00.If he doesn't want the DVD,he needs to send the DVD back or he is deemed to have accepted it.