You are presented with the quiz "What kind of circulatory system do arthropods have?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "mollusks have a circulatory system with one or two hearts that pump blood" and "arthropods and most mollusks have an open circulatory system". 

So, what's the best answer to the question?


 

 open          