What Was the Significance of Moscow's Marble-Lined Subway

What was the significance of Moscow's marble-lined subway?

A) It proved that party elites never advanced higher than the middle class.
B) It was meant to serve as a sign of Communism's promise to bring ease and beauty to the masses.
C) It demonstrated that industrialization had not yet reached the Soviet Union, even after the Five-Year Plan.
D) It marked the successful completion of Stalin's second Five-Year Plan well ahead of schedule.
E) It demonstrated that workers were rarely featured or used in Soviet Union propaganda.