What three parts of the body are fully functioning at birth?

The correct answer identifies the brain, heart, and spinal cord as the three parts of the body that are fully functioning at birth.

At birth, the brain is developed enough to manage basic bodily functions and reflexes, which are crucial for survival. The heart is fully operational and is pumping blood effectively to support the newborn’s circulation and provide oxygen to the body. The spinal cord, as part of the central nervous system, is also developed enough at this stage to facilitate reflex activities and motor coordination in the newborn.

In evaluating the other options, it's important to note that while the kidneys play a role in filtering blood, they are not fully functioning in terms of regulating bodily functions at birth. The lungs are involved in gas exchange, but their full functionality develops after birth with the transition to breathing air. The liver, though present and functioning to some degree, is not fully mature at birth in the same way that the brain, heart, and spinal cord are. Therefore, the combination of brain, heart, and spinal cord accurately reflects the fully functioning systems necessary for the newborn’s immediate survival and adaptation to life outside the womb.