Which of the Following Best Describes the Weighted Average Cost

Which of the following best describes the weighted average cost flow assumption?

A) Direct materials are added evenly throughout the process
B) Equivalent units of production for conversion costs do not match the physical flow of units
C) Inventory cost layers are kept separate based on the period of production
D) Cost per equivalent unit is calculated by combining costs from both the current and previous periods
E) None of the above