Which Position Describes Karl Marx's View of Religion and Society

Which position describes Karl Marx's view of religion and society?

A) Religion was the key to uniting the Bourgeoisie and the Proletariat.
B) Religion simply kept the Proletariat in their low social class.
C) Religion inspired the Proletariat to work harder while under the rule of the Bourgeoisie.
D) Religion was something only the Bourgeoisie had time to contemplate.