Answer:
I just know the meaning of the word keen
Explanation:
Its a slang term meaning wonderful or splendid.
Majority of people in the Sahel (sub-Saharan region, for example: Chad, Sudan) are employed in agriculture, which is the primary sector in the industry.
So the mistake is: not "secondary" but "primary"
The answer is layer one. It is on bottom, so it would be the oldest.
