**Core Concept**
Rebreathing systems are a type of anesthesia delivery system that allows patients to rebreathe exhaled gases, conserving heat and humidity while minimizing waste gas disposal. These systems rely on the principle of gas absorption and desorption to remove carbon dioxide (CO2) from the rebreathed gases.

**Why the Correct Answer is Right**
The correct answer is related to the mechanism of CO2 absorption in rebreathing systems. Most rebreathing systems use soda lime or baralyme as the CO2 absorbent. These absorbents contain calcium hydroxide and sodium hydroxide, which react with CO2 to form calcium carbonate and water. This reaction is catalyzed by the presence of barium hydroxide in baralyme. The absorbed CO2 is thereby removed from the rebreathed gases, making them safe for the patient to inhale.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the mechanism of CO2 absorption, which is the key feature of rebreathing systems.
**Option B:** This option is incorrect because it does not mention the type of CO2 absorbent used in rebreathing systems, which is essential for their functioning.
**Option C:** This option is incorrect because it does not describe the reaction between CO2 and the absorbent, which is the fundamental process in rebreathing systems.

**Clinical Pearl / High-Yield Fact**
One key point to remember is that the CO2 absorbent in rebreathing systems has a limited capacity and must be replaced regularly to prevent CO2 buildup in the rebreathed gases.

**Correct Answer:** D.