Planes frequently push back from the gate on time but then wait 2 feet from the gate until it is time to queue up for takeoff. This increases fuel consumption and increases the time that passengers must sit in a cramped plane awaiting takeoff. Which of the following performance metrics would, if emphasized in evaluations, incentivize airlines to engage in such practices?

a. A performance metric that measures customer satisfaction, based on customer comfort while on the plane
b. A performance metric that measures timeliness of the flight, where a flight is considered "on time" as long as the flight is boarded and away from the gate by the scheduled departure time
c. A performance metric that measures timeliness of the flight, where a flight is considered "on time" as long as the plane takes off by the scheduled departure time.