The correct answer is starvation.
The Holodomor ( 'to kill by starvation') is the genocide of the Ukrainian nation in 1932-33.
The famine affected many grain producing areas. Although officially the cause for the famine were crops failures, many believe that it was planned and ordered by Joseph Stalin on purpose. He wanted to eliminate the Ukrainian independence movement.
He removed all the remaining stocks of grain, rejected foreign aid to the country and locked its people within the territory of the Ukraine without any alternative food supply.
During the Holodomor, millions of ethnic Ukrainians died of starvation or were murdered by the government.