Concept:The NCBWA pressed for political reforms that gave Africans a voice in colonial governance.Explanation:The National Congress of British West Africa (NCBWA) was formed to demand greater African participation in government.One of its major achievements was campaigning for the elective principle.This principle allowed Africans to elect their own representatives into the legislative councils.Therefore, this achievement directly matches the option about introducing the elective principle.Answer:D. introduction of the elective principles.