Which of the following statements concerning glial cells is true?

Which of the following statements concerning glial cells is true?
  a. Astrocytes are phagocytic cells that remove debris in the central nervous system.
  b. Schwann cells form sheaths around neurons within the central nervous system.
  c. Oligodendrocytes regulate the concentration of neurotransmitters in neurons.
  d. Microglia are involved in the neurological disease multiple sclerosis.
  e. Ependymal cells help produce and circulate cerebrospinal fluid.

Question 2

Which statement about the structure of neurons is true?
  a. Dendrites carry impulses away from the cell body.
  b. Axons may form branches known as collaterals.
  c. Nerve impulses travel down the axon toward the cell body.
  d. Dendrites are often myelinated for faster conduction.
  e. Synapses occur between the cell body and its axon.