This was a fairly popular question and was adequately answered by the candidates. Many were able to identify the Ijo, Urhobo, Itsekiri, etc. as some of the Nigerian groups involved in the legitimate trade.
In the (b) part, however, many candidates failed to understand the difference between slave trade and legitimate trade as they wrote extensively on the effect of  the slave trade. This made them to score low marks..
They were expected to discuss the following effects:

(i) emphasis shifted from the slave trade to the production of
cash crops and raw materials;
(ii) there was importation of European finished goods;
(iii) it ushered in peace in most areas;
(iv) it facilitated the spread of Christian Missionary work into the hinterland;
(v) rise of new wealthy merchants, etc.