Which revolution first convinced u. s officials they had to stop the spread of communism in the western hemisphere? a) the assassination  of rafael  trujillo in the dominican  republic  b) the coup to overthrow juan  bosch in the dominican republic  c) fidel castro's  revolution in cubad) the revolution to overthrow salvador allende in chile 

I believe the answer is: C. Fidel Castro's revolution in Cuba
Prior to this revolution, united states government believed that the communist principles from the soviert union was too extreme for the population in Western hemisphere.
Seeing how fidel castro able to won the cuban revolutionary with this principle make United states became aware of the communism threat in western hemisphere.