"<span>D. Blacklisted workers were viewed as troublesome, untrustworthy, and even dangerous by other employers" is the best option from the list, since the "blacklist" in this sense "flagged" them for future employment. </span>
A revision that would help expand the ideas in this passage can be adding a clear description of Rainsford’s overall conflict. It would be better to include a backstory or a glimpse of the history and relationship between Rainsford and General Zaroff, and why they had a conflict.