Positive-pressure ventilations may be difficult to perform on a premature infant because:

A. alveolar surface tension is increased due to surfactant deficiency.
B. the alveoli are nonfunctional secondary to widespread atelectasis.
C. its trachea is usually underdeveloped and the vocal cords are closed.
D. it is often extremely difficult to maintain an adequate mask seal.

Answer: A. alveolar surface tension is increased due to surfactant deficiency.