challenge: What does Bretschneider's formula generalize?
  
  A. Brahmagupta's formula for the area of a cyclic quadrilateral, which in turn generalizes Heron's formula for the area of a triangle
  B. Heron's formula for the area of a triangle only
  C. The area of a polygon with any number of sides
  D. Brahmagupta's formula for the area of a cyclic quadrilateral only
  Answer: 