Final answer:
By 1900, Russia had expanded its railway lines to approximately 30,000 miles of track, making option b the correct choice.
Step-by-step explanation:
The question refers to the extent of railway lines owned by Russia, a topic relevant to Social Studies, specifically focusing on historical developments in industrialization. Sergei Witte, the Minister of Finance in the 1890s, pushed for significant advancements in the Russian railway system after the country's defeat in the Crimean War. At the end of the Crimean War, Russia had less than one thousand miles of track, however, by 1900, this figure had rapidly increased to about thirty-six thousand miles of rail track.
Thus, in the given options, the closest to the historical figure of railway tracks owned by Russia by 1900 would be 30,000 miles (Option b). This development of the railway system facilitated the exploitation of interior reserves like iron, wood, and coal, although Russia's industrialization level lagged behind Western and Central European countries and the United States into the twentieth century.