Why does the spinal cord have the right number of axons to innervate all the muscle cells?

a. Each muscle cell sends a chemical message telling the spinal cord to make a neuron.

b. The genes cause a certain number of neurons to form and the same number of muscles to form.

c. Immature cells divide, with one daughter cell becoming a neuron and the other becoming a muscle.

d. The spinal cord makes an excess of neurons, but those that fail to innervate a muscle die.