Airlines can provide flights to their employees as no$-$additional$-$cost services that are excluded from employee income when:

$($check all that apply$)-$ the airline ordinarily sells flights to customers $-$ at the time the plane is ready to depart, there are empty seats for the employees to occupy $-$ there is forgone revenue related to the seats that could have been sold to paying customers $-$ the airline permits its employees to book their seats in advance of a flights departure without offering the seats for sale to the public $-$ the employee does not cause any forgone revenue since forgone revenue is considered as an additional cost