Why did the United States become involved in Latin America in the early twentieth century?

Why did the United States become involved in Latin America in the early twentieth century?
 
  a. The U.S. military needed to defend Latin America against Spanish or German threats of invasion.
  b. The U.S. wanted to acquire new territories for American colonial expansion.
  c. The U.S. stepped in because several Latin American countries were chronically behind or in default on their debts.
  d. The U.S. hoped to control the flow of Latin American immigrants into the United States.
  e. Roosevelt's administration wanted to strengthen Latin American democracy.