You will be given a definition of a task first, then an example. Follow the example to solve a new instance of the task.
In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

what is the first event mentioned?, Context: The Russian Revolution is the series of revolutions in Russia in 1917, which destroyed the Tsarist autocracy and led to the creation of the Soviet Union. Following the abdication of Nicholas II of Russia, the Russian Provisional Government was established. In October 1917, a red faction revolution occurred in which the Red Guard, armed groups of workers and deserting soldiers directed by the Bolshevik Party, seized control of Saint Petersburg (then known as Petrograd) and began an immediate armed takeover of cities and villages throughout the former Russian Empire.
Solution: Russian Revolution
Why? This is a good example, and the Russian Revolution is the first event mentioned.

New input: What plain letter is used as an example of obsolete sound clusters?, Context: While Old Czech had a basic alphabet from which a general set of orthographical correspondences was drawn, it did not have a standard orthography. It also contained a number of sound clusters which no longer exist; allowing ě (/jɛ/) after soft consonants, which has since shifted to e (/ɛ/), and allowing complex consonant clusters to be pronounced all at once rather than syllabically. A phonological phenomenon, Havlik's law (which began in Proto-Slavic and took various forms in other Slavic languages), appeared in Old Czech; counting backwards from the end of a clause, every odd-numbered yer was vocalized as a vowel, while the other yers disappeared.
Solution:
e