![](https://cos-cdn.shuashuati.com/pipixue-wap/2020-1230-1107-56/ti_inject-812ce.png)
When using the moving-average cost formula with a perpetual system,
A.
a weighted-average cost is calculated at year end.
B.
a new unit cost is calculated each time a sale is made.
C.
a new unit cost is calculated each time a purchase is made.
D.
a new unit cost is calculated both when a sale is made and when a purchase is made.