Answer:
B but don't be surprised if it is D.
Step-by-step explanation:
Russification was a thorn in the side of the rulers. People do not like giving up their culture. It was a cause.
The cities were poor -- especially after the disaster they suffered in WWI. The nobility was not liked. That was a cause.
Czar Alexander may have been slow to reform, but he was not the main culprit. I think this is an answer you should consider carefully. (B)
I would use the adoption of Marxism. That was not made official until After Lenin came to power. The vocabulary was often used by the leaders, but most of the peasants didn't know it's meaning.
The answer is between B and D. I would pick D, but I think you are intended to answer B.