The text tries to compare WMD with other weapons and methods of war. We need a phrase that can fit a comparison.
A – Wrong
The text does not mention anything about morality of bombs and weapons. However, it is obvious that WMD are morally unacceptable since “200,000 people were killed”.
B – Wrong
Again, we know that WMD is a serious threat, so this is wrong.
C – Correct
The text tries to say that there are other methods of war such as ‘conventional bombing’ which cause more widespread death than WMD.
Therefore, the correct phrase would be “But any idea that ‘WMD’ are unique dangerous is easily disproved”.
D – Wrong
We know they are necessarily devastating given the statistics given.