Which one of the following is an example of a "flexibility" option? a. a company has an option to invest in a project today or to wait a year. b. a company has an option to close down an operation if it turns out to be unprofitable. c. a company agrees to pay more to build a plant in order to be able to change the plant's input and/or outputs at a later date if conditions change d. a company invests in a project today to gain knowledge that may enable it to expand into different markets at a later date e. a company invests in a jet aircraft so that it's CEO, who must travel frequently, can arrive for distant meetings feeling less tired than if he had to fly commercial.