8. Which of the following is an example of an organ? A. Kidney B. Blood cells C. Digestive system D. muscle tissue 9. What do you call an organism composed of only one cell? A. eukaryotes B. prokaryotes C. unicellular D. multicellular 10. Which of the following are group of cells that performs specific functions? A. Organ B. organ system C. tissue D.organism 11. Which does not belong to the group? A. Circulatory system C. Reproductive system B. Respiratory system D. Organ system