The correct answer is B) they promised to further the gains of American companies.
Dictators gained power in South America because they promised to further the gains of American companies.
American companies had many economic interests in many countries in South America. They avoided to directly confront the other country's government. So to protect their economic interests what they did was to support rebellion leader's, promised them to help them assume power in exchange of free operations of their companies in the territory. That was the case in Panama, for instance. Or in Cuba. The same happened in Chile with the assassination of Salvador Allende and Augusto Pinochet assuming the government.