Which of the following is the best explanation for Russia’s entrance into World War 1? A. Russia stood by its one

Which of the following is the best explanation for Russia’s entrance into World War 1?
A. Russia stood by its one dependable ally, Austria-Hungary
B. Russia believed in pan-slavism and wanted t defend the Slavic peoples in Serbia.
C. Russia wanted t avoid facing Germany alone at a later date
D. Russia wanted to punish Serbia for encouraging terrorism
THIS