Final answer:
The Communist Party in the Soviet Union was a powerful organization led by a few elite groups, such as Joseph Stalin, who exerted autocratic control over the country. Not everyone in the country was required to be a member, and due to harsh conditions and totalitarian rule, it wasn't always massively popular.
Step-by-step explanation:
The Communist Party in the Soviet Union was an immensely powerful organization. The most fitting description from your options would be 'a few elite groups became the party's rulers.' This is true because although the Communist Party boasted large numbers, power was mostly consolidated within a few key figures, notably under the autocratic control of Joseph Stalin.
Stalin, serving as the General Secretary of the Communist Party, leveraged his position to control all the appointments within the party, ensuring that people loyal and agreeable to him achieved these posts. From this role, he molded the USSR into a form of totalitarianism, where the government sought to control virtually every aspect of its citizens' lives to achieve their goals.
Contrary to belief, not everyone in the Soviet Union was required to be a member of the Communist Party, and even though it had many members, it was not always exceedingly popular amongst the masses, owing to harsh conditions and authoritarian rule.
Learn more about Communist Party in the Soviet Union