单项选择题
Myelin sheaths on the outsides of many axons are contributed by .
A、 A. the axon itself
B、 B. secretory vesicles
C、 C. Schwann cells
D、 D. the cell bodies of the neuron
Myelin sheaths on the outsides of many axons are contributed by .
A、 A. the axon itself
B、 B. secretory vesicles
C、 C. Schwann cells
D、 D. the cell bodies of the neuron