_____ pairs of cranial nerves and ______ pairs of spinal nerves are present in the human body.

The correct option is B. 12 cranial and 31 spinal.

Option (B):

1. The nerves that originate from brain and the spinal cord form the peripheral nervous system or PNS.
   
2. The nerves originating from the brain are called cranial nerves and the nerves originating from the spinal cord are called spinal nerves.
   
3. There are 12 pairs of cranial nerves and 31 pairs of spinal nerves.