(i) Mammals have negative pressure breathing.
(ii) The impulses for voluntary breathing are sent by the medulla oblongata.
(iii) The trachea, primary, secondary and tertiary bronchi, and initial bronchioles are supported by incomplete cartilaginous rings.
(iv) The volume of air remaining in the lungs even after a forcible expiration is functional residual capacity.
How many of the above statements are correct?