I would say the correct answer is A. the desire for a constitutional monarchy. Even during the reign of Tsar Alexander I, there were members of the high aristocracy who wished to establish constitutional monarchy and abolition of serfdom. Some of those military officers were even more radical, aiming for a republic - but the majority of them just wanted a constitutional monarchy, the way it functioned in Britain. After Alexander died in 1925 and his heir Constantine refused the throne, the officers realized they had a chance to press their cause and refused to swear allegiance to the new Tsar, Nicholas I. They brought 3,000 soldiers on the streets to protest. However, the Decembrist Revolt was crushed and the rebels sent to Siberia.
