What percent of russians live between the belarus and ukraine borders and the ural mountains?
a. 25 percent
b. 50 percent
c. 75 percent
d. 90 percent

The majority of the Russian population lives between Lithuania, Belarus,  Ukraine borders and the Ural Mountains - for example already 10% to 20% of Russians live in Moscow - so we can reject answers a) and b)

However, i doubt it's 90% - otherwise they wouldn't have built the Transsiberian Railway to Vladivostok - so the correct answer is 75%.