Terminal bronchioles eventually terminate in:
a) alveoli
b) bronchioles
c) main (primary) bronchi
d) glottis
e) diaphragm

A) alveoli

Explanation:

Bronchioles are part of the respiratory system by which air passes from the nose  to the alveoli (air sacs). They are divided  into smaller terminal bronchioles which are  the conducting zone (involved in respiration) and these then divide into the smaller respiratory bronchioles - the beginning of the respiratory region. Terminal bronchioles are the most distant segment of bronchioles which divide to form respiratory bronchioles which contain a small number of alveoli.