A manufacturing firm is able to produce 1,000 pairs of shoes per hour, at maximum efficiency. There are three eight-hour shifts each day. Due to unavoidable operating interruptions, production averages 800 units per hour. The plant actually operates only 27 days per month. What is the theoretical capacity for April? A. 648,000 units B. 240,000 units C. 518,400 units D. 720,000 units