When calculating unit costs under the weighted-average process-costing method, the unit cost is based on: only the current period's manufacturing costs. only costs in the period's beginning work-in-process inventory, a summation of the costs in the beginning work-in-process inventory plus costs incurred in the current period. only costs incurred in previous accounting periods. a summation of the costs in the beginning work-in-process inventory plus costs to be incurred in the upcoming period