Which One of the Following Correctly Describes the Slope of the Aggregate

Which one of the following correctly describes the slope of the aggregate supply curve?

A) Because individual supply curves slope up, the aggregate supply curve slopes down.
B) The slope of the aggregate supply curve is determined by the willingness of consumers to substitute between goods in response to changes in their relative prices.
C) The aggregate supply curve slopes up to reflect the fact that firms are willing to increase output when their selling prices rise but wages do not.
D) The aggregate supply curve slopes up to reflect the fact that firms are willing to increase output when wages rise but their selling prices do not.