Which of the following is the correct definition of the heijunka principle used in the Toyota Production System? A. A part supplied by an outside supplier which indicates the information about the part, the supplier and the quantity for one container. B. The idea of distributing volume and different specifications evenly over the span of production such as a day, a week and a month. C. A rope running along the assembly line over the work area which is pulled when there is a problem during production. D. A way to mistake-proof a process and prevent errors from occuring