The correct option is B Firing which took place during the march organised at Petrograd.
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When Russia was defeated in the Russia-Japan War in 1905, workers organised a huge march at Petrograd on 9 January 1905, demanding political rights and economic reforms. The march was fired at by the soldiers, and hundreds of demonstrators were massacred. This event is known as the "Bloody Sunday". Later, workers organisations called "the Soviets" were formed all over Russia to conduct strikes.