Answer:
d. Failing to narrow his topic
Explanation:
"You could experience a number of problems if your topic is too broad, including:
You find too many information sources and, as a consequence, it is difficult to decide what to include or exclude or what are the most important.
You find information that is too general and, as a consequence, it is difficult to develop a clear framework for examining the research problem.
A lack of sufficient parameters that clearly define the research problem makes it difficult to identify and apply the proper methods needed to analyze it.
You find information that covers a wide variety of concepts or ideas that can't be integrated into one paper and, as a consequence, you easily trail off into unnecessary tangents. "
Reference: University of Southern California. “Research Guides: Organizing Your Social Sciences Research Paper: Narrowing a Topic Idea.” Narrowing a Topic Idea - Organizing Your Social Sciences Research Paper - Research Guides at University of Southern California, 2019