Concept:When converting an active sentence with a modal (like "could") to passive voice, the object becomes the subject, and the structure is: Object + modal + have been + past participle.
Explanation:The active sentence "No one could have anticipated such a diplomatic backlash" has "No one" as the subject and "such a diplomatic backlash" as the object.
To make it passive, the object moves to the front: "Such a diplomatic backlash".
The modal "could" stays, then add "not" because the original was negative ("could not have anticipated").
The main verb changes to "have been anticipated" (past participle of "anticipate").
Thus, the correct passive form is: "Such a diplomatic backlash could not have been anticipated".
Option A drops the "have been" – it changes the tense. Option B uses "have not been" but lacks the modal "could". Option C uses simple past "was unanticipated" – it changes the meaning and loses the modal.
Only option D keeps the exact modal and perfect aspect.
Answer:Option D: Such a diplomatic backlash could not have been anticipated.