a traveller stumbles across the legendary treasure house of ...

a traveller stumbles across the legendary treasure house of the lost city of Tenbar, guarded by two immortals, each standing in front of a door. There is only one problem: behind one door she will find the piles of gold she has heard such incredible stories about; behind the other, poisonous snakes. she knows from the legend that one guard will always tell the truth, and on guard will always lie, but she doesn’t know which is which she can only ask on question of on guard to help he decide which door to open. what should she ask?