Who is Lying?

Only Brad is telling the truth, Amy and Chris are lying.

The way to go about it is to look for a contradiction that proves one person is lying or telling the truth, and then follow the logic from there:

• If Chris were telling the truth (that both Amy and Brad are lying), Amy would be lying. But this would mean Brad is telling the truth, which contradicts Chris’s statement. So Chris must be lying.
• If Chris is lying, Brad must be telling the truth.
• If Brad is telling the truth, Amy must be lying.