Little's Law says:

Inventory (units) = material flow (units/day) lead time (days)

Which of the following is true?

A. Little's law should never be used if material flow (or demand) has any variability.

B. Little's law should be used to estimate inventory levels when average material flow (or average demand) is constant.

C. Little's law is most useful to estimate inventory levels when material flow (or demand) is seasonal.

D. Little's law is most useful to estimate inventory levels when material flow (or demand) is trending up.

E. Little's law provides an exact inventory level to all material flow (or demand) analyses.