Most process costing systems use weighted average process costs. Which of the following is a characteristic of weighted average process costs systems?

a$)$ These systems account only for costs incurred during the current period.

b$)$ These systems are not appropriate for environments that involve mass production.

c$)$ The weighted average process cost system is required by GAAP.

d$)$ These systems do not distinguish between the costs from the prior period and costs incurred during the current period.

e$)$ None of the above is a characteristic of weighted average process costs systems.