Concept:The coastal region of Sierra Leone is one of the wettest parts of West Africa because it receives heavy monsoon rainfall.Explanation:Moist southwest monsoon winds bring rain to the coast for many months each year.As a result, the annual rainfall in coastal Sierra Leone exceeds 4,000 mm.This is higher than rainfall in the interior and makes Sierra Leone the wettest country in West Africa.Therefore, the correct measurement is above 4,000 mm, not 3,000 mm, 5,000 mm, or 6,500 mm.Answer:B. 4,000 mm