Final answer:
The paragraph was included to educate readers on how charcoal is made and its significance, thereby establishing the text as a credible source on the topic of charcoal.
Step-by-step explanation:
The author included the paragraph about charcoal and its composition primarily to provide necessary background information about the material and process by which charcoal is created. This additional context helps us understand what charcoal is and the transformation it undergoes from wood to a tool for drawing, among other uses. It appears that the best selection is c, as this information establishes the text as a reliable source, enhancing the understanding of charcoal's properties and its significance in various applications such as art and iron production.