An expert's opinion provides historical background of an important concept.
Explanation:
The text presented in the question above, presents us information about the labor practices used in the fast food industry adopted in the beginning of the 20th century. To give veracity and relevance to this information, the text presents the report and opinions of Alfred D. Chancler, a business historian. The presence of an expert like Alfred, makes the text more versatile and specific, since we know that an expert will provide true information about these labor practices. Thus, we can state that the text presents evidence developed by an expert, who provides real historical concepts to confirm that the information contained in the text is true.
