Help the detective finalize his dramatic report. Choose the correct phrase to complete the sentence.

_____ the suspiciously loud sneeze from the ventilation shaft, the jewel thieves would have escaped completely unnoticed.

The correct answer is Had it not been for.

This sentence uses an inverted third conditional to describe a past hypothetical situation. "Had it not been for" is the formal, inverted equivalent of "If it had not been for."

"Were it not for" is incorrect because it forms a second conditional, which clashes with the past result "would have escaped." Additionally, the negative adverb "not" must come immediately after the subject ("it"), making "Had not it been for" grammatically incorrect word order.