Answer: C. They tried to stop liberalism from spreading.
Context:
The Congress of Vienna was a gathering of leaders from the European nations that had defeated France and Napoleon -- and France was allowed representation also. (The French Minister of Foreign Affairs, Charles Maurice de Talleyrand-Périgord, had a role there. ) The Congress met from November 1814 to June 1815, and set the tone for European politics in the decades that followed.
The delegates of the Congress of Vienna were interested in creating a balance of power in European politics. They did not want one nation to become too powerful again and press beyond its borders as France had done under Napoleon. The Congress of Vienna emphasized also the principal of "legitimacy" -- trying to put rulers in power that they thought to be the legitimate rulers of nations. (For instance, they restored the Bourbon monarchy in France.) They sought to prevent revolutions and unrest from breaking out again, which meant taking a stand against liberal freedoms such as freedom of assembly and freedom of the press. Conservative monarchs in the 19th century saw such things as a threat to maintaining the established institutions of their kingdoms.