The correct answer is $\boxed{\text{B. 42}}$.
The peripheral nervous system (PNS) is the part of the nervous system that lies outside the brain and spinal cord. It consists of nerves that connect the central nervous system to the rest of the body. The PNS is divided into two parts: the somatic nervous system and the autonomic nervous system.
The somatic nervous system controls voluntary movement. It consists of nerves that connect the central nervous system to the skeletal muscles.
The autonomic nervous system controls involuntary functions, such as heart rate, blood pressure, and digestion. It consists of two divisions: the sympathetic nervous system and the parasympathetic nervous system.
The sympathetic nervous system is activated in response to stress. It causes the heart rate to increase, the blood pressure to rise, and the pupils to dilate.
The parasympathetic nervous system is activated when the body is at rest. It causes the heart rate to slow down, the blood pressure to lower, and the pupils to constrict.
There are 31 pairs of spinal nerves and 12 pairs of cranial nerves. The spinal nerves are all part of the somatic nervous system. The cranial nerves are part of both the somatic and autonomic nervous systems.
The total number of pairs of peripheral nerves in man is 42.