Which one of the following scenarios represents the use of a kanban to reduce inventories?

Which one of the following scenarios represents the use of a kanban to reduce inventories?
 
  A) A supervisor tells the operators to stay busy and start producing parts for next month.
  B) A supplier work center signals the downstream workstation that a batch has been completed.
  C) A supervisor signals to several work centers that the production rate should be changed.
  D) A customer work center signals to the supplier workstation that more parts are needed.
  E) An operator asks the next station's operator to help him fix his machine.