The Muslim population of Moscow:

a. has an ever increasing number of mosques in which to pray
b. thrives on the melting pot ideals instilled during the Communist era
c. is largely illegal or undocumented, and almost entirely Post-Soviet
d. includes immigrants from Uzbekistan and Kyrgyzstan

a. has an ever increasing number of mosques in which to pray

Explanation:

Russia has about one million Muslim resident s and Moscow has about 300,000 permanent Muslim population and about 1.5 million of them are migrants. And huge numbers are found in the mosques that come to pray and the city had four major mosques for them and they represent the Islamic culture in Russia and is second most widely prepossessed religion.