Which institution did the Tsarist government suspend on 25 February 1917?

Correct answer: Duma

The Tsarist government suspended the Duma on 25 February 1917. The Duma was the elected legislative assembly created after the 1905 Revolution, although its powers under the tsar remained limited. Suspending it during a rapidly developing crisis showed that the government was rejecting even the available constitutional channel instead of negotiating with representatives. Option C is correct. The Petrograd Soviet was formed or became prominent during the revolutionary upheaval, not the institution suspended by the tsar on that date. The Red Army was established after the revolution, and the Cheka was created later by the Bolshevik government as a security organisation. Thus the Duma best fits both the date and the political context.