The objective by which Ellen and her co-workers will benefit the most largely depends on their specific needs and circumstances. However, generally speaking, if they are seeking to improve their working conditions, wages, or job satisfaction, the most immediate and tangible benefits would likely come from:
A. Economic reason
This includes benefits related to better wages, benefits, and working conditions that unions typically negotiate on behalf of their members.
If job security is their primary concern (e.g., in a volatile industry), then B. Job security might be the most relevant option.
Ultimately, it depends on the context and priorities of Ellen and her co-workers. If they are focused on securing stable employment and benefits, then job security could also be a strong contender.