If the Marginal Product of Labour Increases, the Firm's Demand

If the marginal product of labour increases, the firm's demand for labour curve

A) might shift leftward or rightward depending on whether the demand for the firm's product is elastic or inelastic.
B) does not shift but there is a movement along it.
C) shifts rightward.
D) does not shift, and there is no movement along it.
E) shifts leftward.