challenge: What did Stephen Waxman discover about nerve fibers as a student in the 1960s?
  
  A. They are only found in the central nervous system
  B. They can function as 'delay lines', carrying information at less-than-maximal velocity
  C. They always transmit nerve impulses at the maximum possible velocity
  D. They only transmit nerve impulses in one direction, from the brain to the muscles
  Answer: 