Answer:
The correct answers are:
a) A. An economy's price level.
b) A. As the price level rises, firms expand their production because they can sell their output for more money.
Step-by-step explanation:
On the one hand, in this type of economic model, the aggregate supply and demand represent the economy's price and quantity level regarding the output of the country as a whole. Therefore that in the vertical axis of the diagram the curves measures the price level of the economy and in the horizontal axis the curves measure the output that the economy produces at that given price.
On the other hand, the slope of the aggregate supply is upward because of the same reason as it is in the supply curve, because of the law of the supply, that states that there is a direct relationship between the price of the good an its quantity offered. Thefore that when the price level rises the firms will produce more because they can sell their production at a higher price.