1st Guard: Always lies all the time.
2nd Guard: Always tells the truth all the time.
3rd Guard: 75% probability of telling the truth.
4th Guard: 50% probability of telling the truth.
5th Guard: 25% probability of telling the truth.
By asking a single question to one guard of your choosing (although you don't know which is which), find which door has the highest probability of being safe.
The guards that lie, they lie about which door is safe, and they do not lie about other things.
For example, if a lying guard was asked "Is your door safe?", he would lie about this, but if a lying guard was asked, "Are you a liar?", he would admit that he's a liar.