In the Thirteenth Century,Moscow Became an Important Center Because

In the thirteenth century,Moscow became an important center because:

A) Muscovite dukes conquered much of Siberia.
B) it became a center of trade for both eastern and western merchants.
C) it became a tribute-collecting center for the Mongol Khanate.
D) it became a leading intellectual center for the study of Greek texts.
E) it became the site of an annual meeting for the leaders of various Mongol territories.