OG详解-OG6 文法 Q30

Choice C is the best answer. The sentence indicates which classification category most routine diplomatic correspondence belongs in, explaining that it is classified as Confidential because it has the potential to damage national security if disclosed.
Choice A is incorrect. While the sentence makes a claim about information classified as Confidential, it doesn’t indicate which category routine diplomatic correspondence belongs in. Choice B is incorrect. The sentence makes a generalization about how routine diplomatic correspondence is classified; it doesn’t indicate which classification category the correspondence belongs in. Choice D is incorrect. This sentence explains that routine diplomatic correspondence could affect national security if disclosed; it doesn’t indicate which category of sensitive information this correspondence belongs in.