You are presented with the question "What kind of circulatory system do arthropods have?" and the following answer choices: 
- open
 - toads
 - closed
 - porous
 - fluid
 - H 2 O
 - tissue
 - koalas

Now knowing that mollusks have a circulatory system with one or two hearts that pump blood and arthropods and most mollusks have an open circulatory system, choose the best answer.


 

 open        