The phrase in bold in the sentence "No unauthorized personnel were permitted close to the launch pad" is an adverb phrase. Option A is correct.
An adverb phrase is made up of one or more words. The phrase is headed by the adverb and can appear alone or it can be modified by other words.
Adverb phrases most commonly used to modify verbs in a sentence.
Adverb phrases typically answer the questions how, where, why or when something was done.