Final answer:
To effectively research the Oklahoma Land Rush, the most significant question is how it impacted local communities, as this uncovers the event's extensive consequences.
Step-by-step explanation:
When studying the Oklahoma Land Rush, the most important question to guide additional research for Paul would be option B: How did the Oklahoma Land Rush impact the local communities? This question encompasses the broader implications of the event, including the social, economic, and political effects on both the settlers and the Native American populations. Understanding the motivations (A), timeline (C), and location (D) are also key pieces of information, but the impact on local communities is more significant in understanding the long-term consequences and historical importance of the Oklahoma Land Rush.