Aggregate supply can be defined as the total quantity of output (i.e. real GDP) that firms will produce and sell. It is a concept similar to "regular" supply (the supply of a specific good or service in a specific market), but also different from it in important ways. Which of the following is one way in which aggregate supply is different from "regular" supply? a. Aggregate supply is strongly influenced by government policy, unlike regular supply which cannot be influenced by government policy b. Aggregate supply is not affected by decisions made by companies regarding what to produce and sell, it remains the same as long as their goods or services cost the same c. Aggregate supply is a downward sloping curve, unlike single-market supply which is upward sloping d. Aggregate supply cannot shift, unlike regular supply which does shift under certain circumstances