Explain the statement : "tremble , therefore , tyrants of the world" ? ? someone pls answer fast

What was one of the most important causes of the russian revolution of 1917? a. the german occupation of russia during world war ii b. the bolsheviks execution of czar nicholas ii and his family c. csar nicholas ii refusal to withdraw from world war 1 d. the policy of ethnic discrimination put in place by the duma