For example, carbon monoxide is a deadly gas. History tells me that anybody who directly inhaled it for a whole five minutes straight is dead. Science tells me WHY: about the atoms in it and WHAT makes it deadly. (Kind-of a weird example but it's what came into my head lol. It works)
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Science. You can verify with tests.
You need to separate science and history because I think you have confused them both. If it can be verified by one of the following method then it's science: accurately predict a previously unknown result (can be the past, just need to be unknown), can be repeated with predictable results, can be deducted accurately from a known assumption or fact.
So breathing CO and die in 5min is scientific hypothesis that has been confirmed, not history. It is a test with results. More experiments would confirm it. However, to tell the question WHY then you need a new hypothesis other than breathing CO will kill you.
History is problematic because nobody has a clue what happened. For example, you have a bunch of trials where eyewitness testimonies getting butchered because of something that made the eyewitness unreliable.
Most of history is either written by the victor, remembered by some victim who might put some of their colors into the fact, some records that can be inferred or, rarely, an actual scientific record of careful research.