Dr Sowell Plans to Find All the Research That Exists

Dr. Sowell plans to find all the research that exists on the topic of his literature review. Why might he decide otherwise?

A) He might find it difficult or impossible to locate all relevant studies.
B) He might find that including all relevant studies gives equal importance to both highly valid and poor research.
C) There might be so many studies, it would be impossible for him to include all of them.
D) Any of the above constraints might apply.