In relation to the law of contract, explain what is meant by breach of contract, paying attention to anticipatory breach. (10 marks)

中世纪的西欧流行着一则规矩：我的封臣的封臣，不是我的封臣。这是指[ ]

A．西欧封建等级制度    

B．丕平献土

C．西欧城市复兴      

D．琅城起义