In insects, air enters through a ____ and is delivered to interstitial fluid.

A) lung
B) spiracle
C) anterior air sac
D) posterior air sac
E) gill

In insects, air enters through small pores called spiracles and is then distributed to various tissues and organs via a series of air tubes called tracheae. The tracheae end in small, fluid-filled sacs called tracheoles, which are in direct contact with cells and deliver oxygen to the interstitial fluid. Insects do not have lungs or gills. Anterior and posterior air sacs are not present in insects either.