Select your answer:

Topics:
Vitamins and Minerals Diseases of Digestive System Musculoskeletal Anatomy: Knee Name that Pathogen Neuroanatomy Human Digestive System Teeth & Microbes Degeneration Pathology Food Parts of the Brain Nasal Polyp Bones Anatomy Pathology - Chronic Inflammation Mutations, Replication, and Cancer Immune Cells FactionOther quiz:
Circulation and Excretion › ViewWhat regulates human respiration rate?
A. oxygen levels
B. carbon monoxide levels
C. carbon dioxide levels
Circulatory, Artery, Vein - basics › View
delivers “cleaned” blood from the liver to the heart
A. hepatic portal vein
B. renal vein
C. aorta
D. vena cava