Historically, why has the united states restricted trade to cuba?

a) because cuba is too close geographically to the united states for competition.
b) because the united states did not want the cubans to flood the american market with cuban cigars.
c) because of cuba's communist government and its failed protection of the human rights of cuban citizens.
d) because cuba failed to allow the united states to annex the nation of cuba after the spanish american war.