GMAT Critical Reasoning (CR) | Re: Even in a democracy, it is necessary to restrict

The question means there are 4 assumptions in 5 answers.
I negated all the answers to find the non-assumption answer. If the negation damaged the author's conclusion/position (Dissemination to certain countries, those that are or will be competitors or enemies, should be selectively prohibited. There must, however, be free exchange of scientific information) -> the answer is an assumption -> eliminate it.
The remain is the correct answer.

Thus, I eliminated A,B,D and E, leaving C. Negating
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