Riddle me this

My niece likes to ask riddles and I like tormenting my niece. Hear is a riddle that frustrated her forever, well maybe not forever. More like a day and a half until I finally gave her the answer. See if you have better luck then she did.

You're in a room with two doors, one marked "A" the other marked "B". The room also contains two identical twin brothers, who are also dressed exactly the same and know everything about each other. On the wall is a sign that explains that one door leads to freedom, while the other leads to immediate and painful death. The sign also explains the two brothers know which door leads to freedom and which leads to death. However, it also says that one brother always tells the truth, while the other always tells a lie. In order to choose the correct door you are allowed to ask one brother, and one brother only, just one question. What question do you ask to determine which door leads to your freedom?

Well, good luck. I might give you the answer tomorrow. More likely I'll post it in a month or two. Hey, you never know.

Keep watching this space.