Answer:
A. Atheism
Explanation:
The pre-revolution Russian state was deeply integrated with the Orthodox Church. As an ally of the Tzars, the church was a natural target for the Bolsheviks.
As per Wikipedia: Thus the USSR became the first state to have as one objective of its official ideology the elimination of existing religion, and the prevention of future implanting of religious belief, with the goal of establishing state atheism (gosateizm).
