People in sahel usually work in secondary industry wheres the mistake

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"

B.a pop up at ion changes in response to a change in the environment.

Answer the zagros mountains, stretch across western iran and are located next to the khuzestan plain; answer( zagros mountains