This type of source would be
"books of more than one volume"
It appears to be a 4-volume series regarding Southern Rock Opera. We cannot infer that its an anthology, which is a number of collected works within the same genre (such as a 70's rock greatest hits collection), and there are more than one author listed. We also do not know which edition it is.
Answer:
b. Data correlation
Explanation:
Data correlation represents a statistical relationship between two types of data.