challenge: What is the basis of the technique used in Grassmann–Cayley algebra?
  
  A. Descartes' work on analytic geometry and Riemann's work on differential geometry
  B. Grassmann's work on exterior algebra and Cayley's work on matrices and linear algebra
  C. Euler's work on calculus and topology
  D. Newton's work on classical mechanics and Gauss' work on number theory
  Answer: 