challenge: What was the estimated height of the giant bird Eleutherornis?
  
  A. Up to 3 metres (9.8 ft) tall
  B. Up to 2 metres (6.6 ft) tall
  C. Up to 1 metre (3.3 ft) tall
  D. Up to 1.5 metres (4.9 ft) tall
  Answer: 