This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Which of the following makes up the extracellular fluid? 
Select and explain. 
A. Interstitial fluid, B. Blood plasma, C. Both of the above, D. None of the above
C: Both of the above
Answer: C: Both of the above 
Explanation: In animals with a closed vascular system, the ECF is divided into two components: the interstitial fluid and the circulating blood plasma. The plasma and the cellular elements of the blood, principally red blood cells, fill the vascular system, and together they constitute the total blood volume. The interstitial fluid is that pa of the ECF that is outside the vascular system, bathing the cells. Ref: Ganong's Review of Medical Physiology 23rd edition, Chapter 1.