Which event changed the February movement from mere protest into a power crisis?

Correct answer: Soldiers' mutiny and coming to the side of people

The governing concept is the decisive role of military defection in a revolutionary crisis. Demonstrations can remain limited if the armed forces continue to obey the government, but a soldiers’ mutiny removes the regime’s coercive support. When soldiers in Petrograd refused to fire on demonstrators and joined or supported the people, the Tsarist government could no longer reliably enforce its orders. This transformed unrest into a direct struggle over political authority and made the fall of the regime possible. Option A is correct. The construction of a palace, a trade agreement, or a church meeting would not transfer military loyalty or immediately undermine state power.