Fact 1: Fish have a circulatory system with a two-chambered heart.

Fact 2: Birds also have four-chambered hearts.

Given the two facts above, answer the question "What aspect is different for Bird and fish hearts" with the following options: 
- circulatory systems
 - matter vibrating
 - tissue
 - it keeps an organism warm
 - members of their own species
 - heat produced
 - blood
 - type of organs


 

 circulatory systems        