Sorry for the other guy. He was rude. Here's the answer:
Animals excrete CO2 by cellular respiration. Since any living things besides plants can't break down CO2, it just gets put back into the environment. I hope I helped you :)
I believe the answer would be B. someone correct me if I'm wrong.
A. It has organelles enclosed in membranes
1.The enzyme pepsin.Pepsin breaks down proteins in the stomach
2 Im pretty sure its the duodenum and the ileum