Other things the same, what happens in the short run to the price level and quantity of output when the aggregate demand curve shifts to the left?

Which of the following statements is TRUE?

A) The presence of positive economic profit in a perfectly competitive market is consistent with the characteristics of a long-run competitive equilibrium. B) When firms in a perfectly competitive market incur economic losses, some will exit in the long run, thereby shifting the industry supply curve rightward. C) If a profit-maximizing firm in a perfectly competitive market is making an economic profit, then it must be producing at a level of output where price is greater than average total cost. D) If a profit-maximizing firm in a perfectly competitive market is incurring an economic loss, then it must be producing at a level of output where price is greater than average total cost.

Which of the following would shift the entire supply curve for electricity to the left?

a. a decrease in the price per unit of electricity b. a decrease in the price of coal used to generate electricity c. new EPA regulations that force the closing of the worst polluting coal-burning power plants d. a decrease in the price of alternative forms of energy e. a technological improvement that reduces the cost of producing electricity