问题详情

Peter, David and Paul said following sentences: Peter: David is a liar, Paul always tells the truth. David: Peter is truthful. Paul: David is a liar, Peter is truthful. Two of these men always tell the truth, one of them sometimes tells the truth and sometimes lies. Which of these men is a liar？
A．Peter
B．David
C．Paul
D．Not sure此题为多项选择题。请帮忙给出正确答案和分析，谢谢！