Choice "C" is correct. Opportunity cost is the potential benefit lost by selecting a particular course of action. If idle space has no alternative use, there is no benefit foregone; opportunity cost is zero.Choice "b" is incorrect. Opportunity costs are not recorded in the accounting records.Choice "d" is incorrect. Opportunity cost is the potential benefit lost by selecting a particular course of action.Choice "a" is incorrect. Opportunity costs do not represent actual cash outlays.