The north of which country falls within the Sahel?

Option A

The Sahel is a transitional ecoregion west-east across the centre of Africa between the wooded Sudanian Savanna to the south and the Saharan desert to the north. The other countries in the question lie either too far north or too far south.

The Sahel part of Africa includes from west to east parts of northern Senegal, southern Mauritania, central Mali, northern Burkina Faso, the extreme south of Algeria, Niger, the extreme north of Nigeria, the extreme north of Cameroon and Central African Republic, central Chad, central and southern Sudan, the extreme north of South Sudan, Eritrea, and the extreme north of Ethiopia.