The correct answer is C. Water
Step-by-step explanation:
Echinoderms are invertebrate marine animals mainly characterized for being hard or spiny on the outside, examples of echinoderms include starfish and sea cucumbers. These animals are highly particular not only because of the way feed and look but also due to their vascular system, indeed the system vascular system of echinoderms pumps seawater instead of blood as in mammals and because fo this is known as a water vascular system that makes water flow in the body of echinoderms. Therefore, the circulatory fluid in echinoderms is water.