challenge: What was the top speed of the Herluf Trolle-class coastal defence ships?
  
  A. 20 knots (37.0 km/h; 23.0 mph)
  B. 18 knots (33.3 km/h; 20.7 mph)
  C. 12 knots (22.2 km/h; 13.8 mph)
  D. 15.5 knots (28.7 km/h; 17.8 mph)
  Answer: 