Which of the following best describes a futures contract? a. The right to buy or sell a specified quantity of a particular asset during a given period at the spot price. b. A standardized obligation to buy or sell a specified quantity of a particular asset during a given period for a given price. O c. An option to buy or sell a specified quantity of a particular asset during a given period for a given price. d. A standardized obligation to buy or sell a particular asset in a specified quality at a future time, place, and unit price.