challenge: What is the Kulkarni-Nomizu product used for in Riemannian geometry?
  
  A. To construct new contravariant 2-tensors
  B. To construct new tensors from existing tensors on a Riemannian manifold
  C. To construct new symmetric covariant 3-tensors
  D. To construct new 1-tensors from existing 1-tensors
  Answer: 