How did Stalin rule the Soviet Union?

Explanation:

Stalin is well known Communist, he used terror, killings, and threats to carry out to keep the people he was in charge of in check.

might be agreeing to participate ethically with other european nations in the slave trade

or notifying other european nations when taking possession   of african territories

offline recommendation systems option b

because recommendation systems produce a list of two ways

1. through collaborative filtering

or

2. through content-based filtering