Respuesta :
Answer: desertification
Explanation:
Just open up the picture below for explanation.

The reason why Africans have not been able to farm or herd as much in the Sahel is Desertification.
What is desertification?
This is a phenomenon where lands that are close to dry areas such as deserts, suffer from land degradation which makes it hard to engage in agricultural activities on the land.
The Sahel is next to the Sahara and as a result of desertification, less crops grow there which makes herding difficult.
In conclusion, option A is correct.
Find out more on Desertification at https://brainly.com/question/2426422.