This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Misc., Subject name: Physiology
If a region or compartment is in a steady state with respect to a particular substance, then: 
Select and explain. 
A. The amount of the substance in the compartment is increasing, B. The amount of the substance in the compartment is decreasing, C. The amount of the substance in the compartment does not change with respect to time, D. There is no movement into or out of the compartment
C: The amount of the substance in the compartment does not change with respect to time
Answer: C: The amount of the substance in the compartment does not change with respect to time 
Explanation: Ans. C. The amount of the substance in the compartment does not change with respect to timeIn a steady state, the amount or concentration of a substance in a compartment does not change with respect to time. Although there may be considerable movements into and out of the compartment, there is no net gain or loss. Steady states in the body often do not represent an equilibrium condition, but they are displaced from equilibrium by the constant expenditure of metabolic energy.