Choose the item that best describes the economic characteristics of Marginal costs:

		A.The cost of including one extra child in a day-care center.
		B.The cost of merchandise inventory purchased five years ago. The goods are now obsolete.
		C.The cost of feeding 300 children in a public school cafeteria is $450 per day, or $1.50 per child per day.
		D.The management of a high-rise office building uses 3,000 square feet of space in the building for its own administrative functions. This space could be rented for $30,000.
		E.The cost of building an automated assembly line in a factory is $700,000; a manually operated assembly line would cost $250,000.