You are on an island that is inhabited by only two tribes. One of the tribes always tells the truth, and one of the tribes always lies. You have two doors in front of you - one opens up to great treasure and the other opens up to certain death. You need to open up one of the doors. Only the tribes know what is behind the doors, but you don't know which tribe is which. You can only ask one question of one of the tribes. What question do you ask?