A firm practices a level strategy based on the next year's quarterly demand. With an initial inventory level of 0 , demand over the next four quarters is estimated to be 600,800,1000, and 1200 . Inventory carrying cost equals $10 per unit per quarter. Over the next year, what will be the sum of inventory carrying costs? A) $0 B) $36,000 C) $10,000 D) $4,000 E) $9,000