For a Given Firm, Whenever the Ratio of Marginal Product

For a given firm, whenever the ratio of marginal product to input price differs across inputs,

A) the market will adjust the price of the higher priced input.
B) it will always be possible to make a cost-saving substitution in favor of the input with the lower MP/P ratio (except in the case of corner solutions) .
C) it will always be possible to make a cost-saving substitution in favor of the input with the higher MP/P ratio.
D) the market will adjust the price of the lower priced input.