The Assembly Department of Smart Computers had 500 units of beginning inventory in the month of September and 2,000 units were transferred to it by the Production Department. The Assembly Department completed 1,000 units during the month and transferred them to the Packaging Department. Calculate the total number of units accounted for by the Assembly Department if it had 1,500 units in ending inventory.

A) 1,500 units

B) 2,000 units

C) 500 units

D) 2,500 units