Mary Ann and Donna Provide Lawn Mowing Services in a Perfectly

Mary Ann and Donna provide lawn mowing services in a perfectly competitive market.When they began their operations,the market rate for mowing lawns was $50 per lawn.After the price increased to $60,they were willing to work on Saturdays as well.Their response to the price change will be shown by _____

A) a rightward shift of the market supply curve.
B) a leftward shift of the market supply curve.
C) an upward movement along their firm's marginal cost curve.
D) a downward movement along their firm's marginal cost curve.
E) a rightward shift in the market demand curve for mowing lawns.