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

Question $13$ options:

A supervisor tells the operators to stay busy and start producing parts for next month.

A "supplier" work center signals the downstream workstation that a batch has been completed.

A supervisor signals to several work centers that the production rate should be changed.

A "customer" work center signals to the "supplier" workstation that more parts are needed.

An operator asks the next station's operator to help him fix his machine.