Which best describes the thirteenth century invaders and conquerors of Russia? A) They were Byzantines who introduced serfdom, raised taxes, and massacred thousands of people. B) They were Muslims who introduced Islam and brought Arabic art, science, and architectural styles. C) They were Chinese armies who gained trust by using native Russians in government and adopted Russian customs. D) They were Mongols who leveled cities, looted treasures, and massacred entire populations.