A firm had no work in process at the beginning of a month. It transferred 4,000 units to finished goods during the month, and 500 units were still in process at the end of the month. Equivalent production for the month was 4,400 units. At what stage of completion were the unfinished units at the end of the month?
A. 67 percent
B. 75 percent
C. 20 percent
D. 80 percent