Islamic Caliphates spread Islam throughout the region during the post classical period and this statement best explains why Islam is an important religion in many parts of northern Africa today. The correct option among all the options that are given in the question is the third option or option "c".<span />
metallurgy is your answer
The "study of metals and the process of refining (them)...."
Note that it says metal. Metallurgy has the word "Metal" in it, and so is most likely your answer (and is your answer).
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The answer is d. I hope that this was helpful