What Did Denis Diderot and Paul D'Holbach Argue That Led

What did Denis Diderot and Paul d'Holbach argue that led to their conclusion God was unnecessary?

A) Matter worked mechanically through the laws of physics
B) Matter and motion were eternal
C) God as a first cause also would have to be considered a contingent being, thus the universe could have no noncontingent being, that is, God
D) They argued, God was dead