challenge: What does the method of Lagrange multipliers seek in the case of multiple constraints?
  
  A. A point where the gradient of f is a multiple of any single constraint's gradient
  B. A point where the level set of f is perpendicular to all the constraints
  C. A point where the gradient of f is a linear combination of all the constraints' gradients
  D. A point where the level set of f is parallel to one of the constraints
  Answer: 