The correct answer is option 1: St. Petersburg. The Russian Revolution began in St. Petersburg (now known as Petrograd). The revolution started with the February Revolution in 1917, which led to the abdication of Tsar Nicholas II and the end of the Romanov dynasty. St. Petersburg was the capital of Russia at the time and a center of political discontent and revolutionary activity. The revolution in St. Petersburg quickly spread to other parts of the country, leading to the October Revolution later that year, which brought the Bolsheviks to power and ultimately resulted in the formation of the Soviet Union. St. Petersburg played a pivotal role in the Russian Revolution and remains an important historical city in Russia.