Fish have a circulatory system with a two-chambered heart, and birds also have four-chambered hearts. Given these facts, what aspect is different for Bird and fish hearts among 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        