challenge: Who were the Yale psychologists behind the monograph that introduced the frustration–aggression hypothesis in 1939?
  
  A. Sigmund Freud and B.F. Skinner
  B. Erik Erikson and Lev Vygotsky
  C. John Dollard, Leonard Doob, Neal Miller, O. H Mowrer, and Robert Sears
  D. Albert Bandura and Jean Piaget
  Answer: 