challenge: What was considered during the rebuilding of the railway line from Waunfawr to Rhyd Ddu between 2001 and 2003?
  
  A. Removing the existing loop at Plas-y-nant
  B. Establishing a temporary terminus at Plas-y-nant
  C. Establishing a new railway line to Plas-y-nant
  D. Extending the existing engineer's siding at Plas-y-nant
  Answer: 