Concept:The first inter-territorial political movement in British West Africa during the 1920s was the National Congress of British West Africa (NCBWA).
Explanation:The NCBWA was formed in 1920 to unite all British West African territories, including Nigeria, Ghana, Sierra Leone, and The Gambia.
Its main goal was to fight colonial policies and push for political and economic reforms.
The Aborigines Right Protection Society was a Ghanaian pressure group, not an inter-territorial movement.
The West African Youth League was founded later, in the 1930s, by I.T.A. Wallace-Johnson.
The West African Students Union was a student organization based in London.
Among the given options, only the National Congress of British West Africa matches the description of a 1920s inter-territorial movement.
Answer:C. National Congress of British West Africa