Which One of the Following Statements Is Best

Which one of the following statements is best?

A) Two operating rules for the Kanban system are (1) the container size should be equal to at least seven days of supply and (2) each container must have a Kanban card.
B) The Kanban system is more effective when the assembly schedule calls for small lots and does not fluctuate much from day to day.
C) The number of Kanban cards should be equal to the desired safety stock times alpha.
D) Supplier performance is much more important in U.S.environments than such factors as lot sizes,scrap losses,and worker flexibility.