Answer;
A. Gas exchanges takes place by diffusion.
B. It is an open system.
Step-by-step explanation;
- Most molluscs and arthropods have an open type of circulatory system.
- Open circulatory systems pump blood into a hemocoel with the blood diffusing back to the circulatory system between cells.
- Blood is pumped by a heart into the body cavities, where tissues are surrounded by the blood.