Lenin's most significant contribution to Marxist thought was the development of the idea that

Without a revolutionary theory, there can be no revolutionary movement

Explanation:

Lenin's most significant contribution to Marxist thought was the development of the idea that "Without a revolutionary theory, there can be no revolutionary movement."

This evident in the fact that it was the Lenin and the followers of his philosophy who used the idea to bring about the first successful communist revolution in Russia around 1917.

This eventually led to the creation of the first contemporary totalitarian state in the Soviet Union.

answer: d. geography : )