Which of the Following Best Explains 'Kanban

Which of the following best explains 'Kanban'? 

A)  A form of JIT based upon fixed volume lot delivery. 
B)  The exact same as just-in-time (JIT) . 
C)  Where the ordering costs per unit is lowest. 
D)  A form of JIT based upon fixed volume lot delivery. When a lot is used, the kanban (card) will be sent to the supplier as a signal to replenish that lot