Question

this reef shark has gills, not lungs. its gills look like slits on the side of its body.
the reef sharks gills are part of both its excretory system and its respiratory system. the reef sharks gills and other animals lungs have similar jobs.
which of the following is a function of gills?
they pump blood throughout the body.
they release carbon dioxide waste into the water.
they filter waste out of the blood to produce urine.

Explanation:

Gills are part of the respiratory system. In respiration, carbon dioxide (a waste product) is released. Lungs (in other animals) and gills have similar jobs. Pumping blood is the heart's function. Filtering blood for urine is the kidney's role.

Answer:

They release carbon dioxide waste into the water.