As neeshpal said, the answer should be C.
I have a Q here
why not A-subjunctive?
One of the reasons is because it isn't correct to "prohibit something (to
) be disclosed." It should be "from being disclosed" instead.
E is incorrect for the same reason as A.
Both B and D are incorrect because they use the plural pronoun "they" to refer back to the singular noun "employee."
C is correct.