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.
how do the reef sharks gills help remove waste?
they release carbon dioxide waste into the water.
they break down waste and release it into the blood.
they filter waste out of the blood to produce urine.

Explanation:

The gills of a reef shark are part of its respiratory system. In the respiratory process, carbon dioxide (a waste product) is released. Just like in animals with lungs (where carbon dioxide is exhaled), in sharks (with gills), carbon dioxide waste is released into the water. Breaking down waste and releasing it into the blood is not the function of gills. Filtering waste out of the blood to produce urine is a function related to the excretory system (like kidneys in some animals), not the gills.

Answer:

They release carbon dioxide waste into the water.