Final answer:
An advantage of an open circulatory system is reduced energy expenditure on its maintenance, because it is simpler than the closed circulatory system, requiring less energy for a body to sustain it.
Step-by-step explanation:
The correct answer to the question is d) Reduced energy expenditure on circulatory maintenance. An open circulatory system is less complex than a closed circulatory system, which is characterized by blood that is contained within blood vessels and circulated efficiently throughout the body. In contrast, an open circulatory system involves the pumping of blood into a hemocoel, allowing it to flow freely around the organs and tissues before returning to the heart through ostia. This lack of complexity requires less energy for an organism to maintain its circulatory processes. Therefore, an open circulatory system is advantageous because it necessitates reduced energy expenditure for circulation compared to the more structured and controlled closed system.