Journal entry 7 April 010

This is a cool riddle.

A man was about to be executed by the king, the king decided to give hm one chance to live. He was taken by a guard. Thee was a life door and a death door. And there was a guard standing in front of each door. One guard always tells the truth and one guard always lies. The Man does not know who tells the truth and who lies, and he dosent know which door is the life or death door. He was allowed to ask one question to 1 guard only. Using the answer he shall find out which door is which. Eventually he chose the life door and lived, what was the question that he asked the guard ??

Solve it