Early initiatives by the United States under Truman, Eisenhower, and Kennedy received broad support. Only two members of the United States Congress voted against granting Johnson broad authority to wage the war in Vietnam, and most Americans supported this measure as well.
Does this answer your question?
It is not an economic activity - it's linguistic in nature, not economic.
It is not linguistics either - linguistics is a scientific discipline.
It's also not a culture region - this would be a kind of region, and a region is not the same as spread of culture.
The correct answer is "a) cultural diffusion.