What name do economists have for a cost that has already been committed and cannot be recovered?

Which of the following is least likely to increase the demand for airline tickets?

A) A Department of Energy order closing gasoline stations on weekends. B) A Department of Energy order restricting gasoline sales on odd and even-numbered days of the month to cars with odd or even final digits in the license number C) A fall in the price of airline tickets D) A rise in the price of gasoline E) An excellent record of airline safety

What is economic surplus? When is economic surplus at a maximum?

What will be an ideal response?