Review the map showing the gold–salt trade route during the time of the Ghana Empire. Why was the West African kingdom of Ghana an important trade center?

It controlled the entire Sahara desert.
It controlled all territory surrounding the Niger River.
It controlled trade routes between major waterways.
It controlled the coastline of West Africa.

Ascientist performs an experiment where she measures the mass of a piece of metal, pours acid onto the metal, washes the metal, and then re-measures the mass of the metal. the scientist repeats the experiment several times, each time increasing the amount of acid used. the dependent variable in the experiment is the: initial mass of the metal final mass of the metal amount of acid used washing the metal