In a very far land, in addition to the liars (who always lie), knights (who always tells the truth) and knaves (who alternate between truth and lies), there are also shays. Shays will tell the truth unless the last person to talk was a liar or a knave who lied.
In that land, there is a very famous doctor that you want to meet. This doctor has his own nurse and his own apprentice. After you get to the doctor's house, you see the three people (the doctor, the nurse, and the apprentice) but you do not know who is what or what types they are. So you ask a few questions:
"Which one of you is a knave?"
A: I'm a knave!
B: I'm a knave!
C: I'm a knave!
"Which one of you is the apprentice?"
C: I'm the apprentice!
B: I'm the apprentice!
A: I'm the apprentice!
"Which one of you is the doctor?"
A: I'm the doctor!
B: I'm the doctor!
C: I'm the doctor!
From those statements can you figure out who is the doctor, nurse, and apprentice?