A says B lies, B says C lies, C says A and B lie. Who lies and who tells the truth?

If A is telling the truth, then B must be lying and C must be telling the truth. If C is telling the truth, A and B must be lying; but this is inconsistent with the initial assumption that A is telling the truth. This implies that A is lying.

If A is lying, then B must be telling the truth and C must be lying. If C is lying, A or B (or both) must be telling the truth. This condition is satisfied since while A is lying, B is telling the truth.

Therefore the answer to the problem is that A lies, B tells the truth, and C lies.