challenge: What modification was made to the headlamps of most serving SAR steam and electric locomotives in the 1970s?
  
  A. Their original large round headlamps were replaced by double sealed-beam automobile headlamps
  B. Their original large round headlamps were retained and the glass was replaced by a metal disk containing single sealed-beam headlamps
  C. Their original large round headlamps were repainted to improve visibility
  D. Their original large round headlamps were replaced by single sealed-beam locomotive headlamps
  Answer: 