The community puzzle thread

[darkknightkryta]

I got another riddle:

You have just been allowed to leave prison.
They give you 2 doors.
One door is freedom, the other door is death.
There is a guard next to each of these doors. One is a liar the other is truthful.
How would you know which door to go through?

There was a question to ask that gives you the answer.  I don't remember what it was.