Which comparison is correct?
a--the spinal cord is like a highway, and the nerves are like the roads that branch off the highway.
b--the spinal cord is like an information center, and the nerves are like the news broadcasts from it.
c--the spinal cord is like the insulation inside a wall, and the nerves are like the outer shell of the wall.
d--the spinal cord is like a power generator, and the nerves are like the power lines connected to it.