challenge: What is the key assumption of the theory of materials with memory, as proposed by Ludwig Boltzmann and Vito Volterra?
  
  A. The local stress value at a time t is independent of the local deformation history
  B. The local stress value at a time t is determined by the remote history of the deformation
  C. The local stress value at a time t depends upon the history of the local deformation up to t
  D. The local stress value at a time t depends only on the current local deformation
  Answer: 