challenge: What was the cylinder size of the LNWR 18in Goods Class steam locomotives?
  
  A. 16 by 20 in (406 by 508 mm)
  B. 18 by 24 in (457 by 610 mm)
  C. 20 by 26 in (508 by 660 mm)
  D. 22 by 28 in (559 by 711 mm)
  Answer: 