Answer:
The sentence that needs revising to eliminate redundancy is " If past history is an indication, the sirens will save hundreds of lives."
Step-by-step explanation:
One of the meanings of the word "history" is a sequence of past events connected to something or someone. We can always assume, thus, that when someone mentions "history", they are talking about the past.
So, when it comes to the sentence we are analyzing here, the use of the words "past history" is redundant. If it is history, it is past.