Answer: Karen is following the use of secondary source.
Explanation:
A secondary source is a source found referenced in another source. Take for instance, if you are reading a research article by Kola (2014) and Kola quotes or refers to
the information previously published by Temi (2006), referring to Temi in your own work would be considered a secondary source—i.e., you are not citing Temi’s original research, but rather Kola’s reference to Temi’s research.