Which of the following explains why the soviet union decided to place nuclear missiles in cuba before the cuban missile crisis? a. the soviet union hoped to use the missiles to threaten cuba's government into adopting communist policies. b. the united states established a blockade around cuba, preventing it from trading with any capitalist country. c. cuba's communist leaders demanded soviet military support after u. s.-trained soldiers had invaded cuba. d. the united nations urged both the soviet union and the united states to provide nuclear technology to poor countries.

C.Cuba's communist leaders demanded Soviet military support after U.S.-trained soldiers had invaded Cuba.

The invasion of US-trained soldiers occurred in 1961 -- The Bay of Pigs Invasion.  Cuban exiles trained by the USA's Central Intelligence Agency aimed to overthrow the communist government of Fidel Castro in Cuba, but failed.

Cuba requested that the USSR, as its communist sponsor, place missiles in Cuba to deter further US-sponsored action against the Castro regime.  That request, coupled with the fact of American missiles that were located in Europe, within striking distance of the USSR, prompted Nikita Khrushchev of the USSR to send the missiles to Cuba.