Concept:An external influence is a foreign group whose contact helped spread a language or culture in the Nigeria area.
Explanation:The Nok civilization was not external because it was an ancient culture already within the Nigeria area.
Egyptian traders and Phoenician explorers had little lasting influence on language spread there.
Arab merchants, however, came into the Nigeria area through trans-Saharan trade routes.
Their long interaction with local communities encouraged cultural and linguistic exchange.
This interaction therefore contributed to the spread of Bantu language in the Nigeria area.
So, among the options, Arab merchants are the correct external influence.
Answer:D. Arab merchants