One reason the ancient kingdoms in western Africa became wealthy was that they developed extensive trade in gold and

Salt

Explanation:

The ancient kingdom of West Africa was widely known to be wealthy through the territory's large deposit of gold. This was the period of the 7th to 14th century, and some empires benefited from this wealth including the likes of the Mali Empire, the Songhai Empire, etc.

The extensive trade in gold and SALT during this period is known as Trans-Saharan trade because it involves mostly the west African countries trading gold in exchange for Salt with the Northern African countries such as Egypt, other desertic regions in Africa.

Hence, in this case, the correct answer is SALT.

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he is known for discovering   the fossil of a female hominin australopithecine   known as "lucy" in the afar triangle region of hadar, ethiopia.

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