Introduction to respiration - class-IX

Read the following four statements carefully.
(i) Ventral respiratory group of neurons of medulla oblongata can cause both inspiration and expiration. 
(ii) The part of the respiratory system starting with the external nostrils up to the terminal bronchioles constitutes the respiratory or exchange part of the respiratory system. 
(iii)  During swallowing epiglottis can be covered by a thin elastic cartilaginous flap called glottis to prevent the entry of food into the larynx.
(iv)  Binding of oxygen with haemoglobin is primarily related to partial pressure of $O _{2}$. 
Which of the above two statements are correct?