The economies of west african nations have been weak since
a. they developed trade imbalances
b. military rulers have taken over
c. they gained independence from colonial powers
d. european traders came to west africa

The answer is    d.  central highlands

Idont know i wonder tthough seems like it will be intristing

Your answer is d. silli hope this ! : ) i left an explanation down below if you need it: a sill forms when hot magma squeezes between layers of rock to form a hardened sheet of rock. a sill is basically a tabular sheet intrusion between old layers of sedimentary rock, volcanic beds, or in the direction of foliation inherent in metamorphic rock. the word sill means a concordant intrusive sheet.