MHB What's the safest way out of these two caves?

[Poirot1]

You must enter one of two caves. One cave leads to certain death, the other to safety. A guard stands at each entrance, one who always tells the truth and one who always lies. You make ask one question to either of the guards. What should you ask?
Not difficult by an means but entertained me when I was younger.

 

[CaptainBlack]

You must enter one of two caves. One cave leads to certain death, the other to safety. A guard stands at each entrance, one who always tells the truth and one who always lies. You make ask one question to either of the guards. What should you ask?
Not difficult by an means but entertained me when I was younger.

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Spoiler

You ask either guard what the other would say if asked which lead to safety, then take the other.

CB

 

[alane1994]

I remember this one... Except when it was told to me, it was TweedleDee and TweedleDum from Alice In Wonderland instead of guards.