What was a major effect of soviet gulags under joseph stalin?

a. soviet infrastructure was improved through slave labor.
b. economic collectivization ended in the rural soviet union.
c. totalitarian states in western europe were weakened.
d. ukraine rejoined the soviet union following the holodomor.

Stalin established forced labor camps known as "Gulogs" which was an acronym for Glavnoe Uprablenie Lagerei, actually it was a government run prison camp where over 39 million people were executed, millions starved or frozen to death.  If you disagreed with Stalin, you were sent to the camps without a trail.  The Gulogs were part of the "Great Terror" that gripped the Soviet country.  Anyone expressing an intellectual thought was considered dangerous and forced to work or shot immediately.  Stalin forced the Soviet people to worship his government, not God.  Farmers who built up their farms were forced to hand them over to Stalin and his centralized control.  Anyone still free had severe food shortages because the food was sold to build more government comforts.
Stalins' mass executions of intellectuals and skilled workers caused the government to become inefficient and industrialization slowed down somewhat.

The answer would probably be "A", since the Soviet infrastructure was improved through the slave labor and the push for industrialization. 

Soviet infrastructure was improved through slave labor

Because broadest terms allows the law flexibility depending on changing society and circumstances.