**Core Concept**
The Mapelson E breathing system is a type of pediatric anesthesia circuit used for delivering oxygen to patients. It is designed to provide a high concentration of oxygen to the patient, while minimizing the risk of rebreathing carbon dioxide. In infants, the Mapelson E circuit is modified to accommodate their unique respiratory needs.

**Why the Correct Answer is Right**
The modified Mapelson E circuit for infants incorporates a **popping valve** to prevent the rebreathing of exhaled gases. This valve is designed to open at a lower pressure than the Mapelson E circuit, allowing for more efficient gas exchange. Additionally, the modified circuit may include a **heat and moisture exchanger** to help maintain a stable body temperature and prevent respiratory complications. The use of a modified Mapelson E circuit in infants is essential for ensuring effective oxygenation and ventilation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not mention the specific modification of the Mapelson E circuit used in infants, which is the incorporation of a popping valve.
**Option B:** This option is incorrect because it refers to a different type of anesthesia circuit, rather than the modified Mapelson E circuit used in infants.
**Option C:** This option is incorrect because it does not accurately describe the modification of the Mapelson E circuit used in infants, which is the use of a heat and moisture exchanger in addition to a popping valve.

**Clinical Pearl / High-Yield Fact**
In pediatric anesthesia, the Mapelson E circuit is often modified to accommodate the unique respiratory needs of infants. The incorporation of a popping valve and heat and moisture exchanger helps to ensure effective oxygenation and ventilation in this population.

**Correct Answer: B. Jackson Rees modification of Mapelson E circuit**