Answer:
D. Who were the key figures that participated in American Revolution.
Step-by-step explanation:
The one crucial part while conducting research is narrowing the topic as a too broad topic may become unmanageable and evoke conflicting opinions. To conduct the research effectively, it is important to narrow the topic and a research question best complements to provide a specific idea which would here be option D as it best serves the purpose of the topic that is American Revolution. The key figures who participated in the American Revolution would contribute to shaping the research and the sources complementing the central argument. This question would assist to focus and emphasize one major idea.