We are told that to maintain military deterrence, a nation would have to be believed to have retaliatory power so great that a potential aggressor nation would have reason to think that it could not defend itself against such retaliation.
It's important to note that it is not necessary for said nation to actually have a retaliatory force that is greater, merely that a potential aggressor has reason to believe that said nation has a retaliatory force that is greater.
Therefore, it is not necessarily true that to be able to maintain military deterrence, a nation MUST maintain a retaliatory force greater than that of any other nation.
That is why answer choice (E) is not correct.
Hope that clears things up! Please let us know if you have any other questions.
