**Core Concept**
The question is testing the knowledge of appropriate methods for transporting newborns, specifically focusing on maintaining their body temperature. This is crucial for preventing hypothermia, which can be life-threatening in newborns.

**Why the Correct Answer is Right**
The correct answer is a radiant warmer or a transport incubator. These devices provide a controlled environment to maintain the newborn's body temperature between 36.5°C and 37.5°C. They work by emitting infrared radiation to warm the newborn's skin, which is an effective and efficient method for temperature regulation. Additionally, these devices often have a clear plastic dome or canopy that allows caregivers to observe the newborn while maintaining a warm environment.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely a blanket or a towel, which are not effective for maintaining a newborn's body temperature during transport. Blankets and towels can become wet and lose their insulating properties, leading to heat loss.
**Option B:** This option might be a car seat, which is not designed to maintain a newborn's body temperature. Car seats can be cold and may not provide adequate insulation, increasing the risk of hypothermia.
**Option C:** This option could be a warming mattress, which is not suitable for transporting newborns. While warming mattresses can be used in hospitals to warm newborns, they are not designed for transport and may not provide a stable or controlled environment.

**Clinical Pearl / High-Yield Fact**
Newborns lose heat rapidly due to their large surface area to body mass ratio and thin layer of subcutaneous fat. To prevent hypothermia, it's essential to use a radiant warmer or transport incubator, and to keep the newborn's head, chest, and back uncovered to allow for efficient heat loss.

**Correct Answer:** C.