If a Competitive Firm Experiences a Shift in Costs of Production

If a competitive firm experiences a shift in costs of production that decreases marginal costs at all levels of output,

A) expanding output levels at any given price will be profitable.
B) producing less at any market price will off-set marginal cost .
C) the firm's marginal cost curve will shift to the left.
D) the firm's demand curve will also shift to the left.