Hi Marie,
I believe that the text is correct as end-expiratory lung volume would be the reserve of air left in the lungs after expiration. This residual volume is important to keep the lungs inflated (reduce change of collapsing). A greater inspiration (“prolonged slow inspiration”) would increase the inspiratory lung volumes, which would influence functional residual capacity after expiration, which improves lung volume at rest and decreases atelectasis (collapse of a lung, or part of a lung, due to the alveoli losing air). The youtube video below explains the different lung volumes.
I hope this helps!
Helen