Final answer:
The correct answer is option B. The function of the water vascular system is moving. It allows echinoderms to move and exert force through their tube feet.
Step-by-step explanation:
The function of the water vascular system is moving. In echinoderms, such as starfish and sea urchins, the water vascular system is responsible for locomotion. The system consists of a central ring canal and radial canals extending along each arm. Water circulates through these structures, allowing for gas, nutrient, and waste exchange. The system enables the organism to move and exert force through its tube feet, which can expand or contract using the hydrostatic pressure in the system.