Final answer:
Russia was considered a multinational empire in its first three centuries because it occupied areas with many different ethnicities, resulting in a vast and diverse empire.
Step-by-step explanation:
In its first three centuries, Russia could be called a multinational empire primarily because B) It occupied areas of many different ethnicities. Both the Russian Empire and the Soviet Union ruled over a large variety of ethnic groups with diverse languages, religions, and cultural practices, spanning from Eastern Europe to the Pacific Ocean. The territory of the Russian Federation was conquered incrementally as the country expanded from the political core around Moscow/St. Petersburg from the 16th through the 19th centuries. By the end of the 18th century, it had grown to include parts of what is now Ukraine, the northern Caucasus Mountains, Central Asia, and even Alaska. This created a vast empire, presenting both administrative and cultural challenges due to the enormous diversity within its domain.