What Is the Primary Reason Why European Russia Has a Higher

What is the primary reason why European Russia has a higher population than Asian Russia?

A) European Russia has historically had an extremely low death rate.
B) Communist government policies forced millions to move to European Russia from Asian Russia.
C) European Russia lost much of its population in World War II.
D) Devastating diseases killed off much of the population of Asian Russia.
E) European Russia is better suited for agriculture and has a slightly milder climate.