A is a clothing seller, from B imported a batch of "elephant skin" pants, but in fact is not made of elephant skin, is a kind of artificial fabric, they said in accordance with the laws of Singapore. When the pants entered the country, customs thought they were made of elephant skin and seized them, then they were burned. Later, customs found out that the pants were not made of elephant skin, but they told A that they could not compensate her. Finally, B wants to sue A, saying that A is improperly suspending the contract. The question is: 1. what principles of contract law can B rely on to avoid breach of contract? 2. what principles of contract law can B rely on to claim compensation like customs (what principles of contract law can customs rely on to avoid liability)?