Final answer:
The most effective research question is 'How have youth advocates initiated widespread change?' since it examines the involvement and impact of youth in advocacy, aligning with the guidelines for creating a significant advocacy project.
Step-by-step explanation:
An effective research question based on the information provided would be one that delves into the specifics of advocacy and its impact on a chosen issue, considering both the conception and execution of promising solutions. Option D, 'How have youth advocates initiated widespread change?' addresses this by exploring the proactive roles that youth take within advocacy, their innovations, and the outcomes of their efforts on a larger scale. It encompasses both the identification of an issue and the active steps taken to propose change, which aligns with the guidelines for brainstorming and developing a meaningful advocacy project as described.