Fact 1: Mollusks have a circulatory system with one or two hearts that pump blood.

Fact 2: Arthropods and most mollusks have an open circulatory system.

Given the two facts above, answer the question "What kind of circulatory system do arthropods have?" with the following options: 
- open
 - toads
 - closed
 - porous
 - fluid
 - H 2 O
 - tissue
 - koalas


 

 open        