Which of the following relating to Shadow Prices are true, when considering a linear programming problem? a) Shadow Prices occur when there is slack available b) There is no binding constraint when a Shadow Price exists. c) The Shadow Price represents the total price a business would pay to obtain an extra unit of a scarce resource d) The Shadow Price is the additional premium above the current purchase price that a business would be prepared to pay to obtain an additional unit of a scarce resource.