The correct answer is C. The tsar abdicated in protest over the failures of the Russian military against the German army.
Explanation
Nicholas II (1868 - 1918) is the name of the last Russian Tsar from 1894 until his abdication in 1917 due to the ruin of the monarchical government, the successive Russian defeats in the First World War, the February Revolution. Additionally, in 1917 the internal situation of Russia was going through a difficult time due to the fact that Russia was losing the war against Germany, and the internal situation was stressed by the nascent revolutions. Therefore, Nicholas II decided to give way to the provisional government thorugh his abdicate. According to the above, the correct answer is C. The tsar abdicated in protest over the failures of the Russian military against the German army.