5$\cdot$108 It is known that the residents of a certain country are either knights or liars, knights tell the truth while liars always lie. We encounter 3 residents of this country $A, B, C, A$ says: “If $C$ is a knight, then $B$ is a liar.” $C$ says: “$A$ and I are different, one is a knight and one is a liar.” Who among the three

people are knights, and who are liars?
[Solution] Let $A$ be a knight. If $C$ is also a knight, then by $C$'s statement being true, $A$ should be a knave, which is a contradiction; if $C$ is a knave, then $C$'s statement is a lie, thus $A$ should also be a knave, which is also a contradiction. Therefore, $A$ is a knave.

From $A$'s lie, we know that $C$ is a knight, and $B$ is also a knight. So $A$ is a knave, and $B$ and $C$ are both knights.