A says, “B is lying, and C is not.”
B says, “A is lying.”
C says, “I’m not lying, and I know D is lying.”
D says, “A and B are lying.”
E says, “B and D are not lying.”
There are three liars. Find them.

B, D and E are the liars.
First, if A was a liar, then C would be a liar. But then D would say the truth, which contradicts A’s statement about B lying. Therefore, A says the truth. That means C also says the truth. You can use logic to prove that this doesn’t make a contradiction.