Which of the following best describes why the Principles of European Contract Law may be applicable to an agreement between two (parties, from different states in Europe, to a contract even if the subject of the contract is for the sale of goods?
选项：

A:It is binding European Union law.
B:The principle of Good Faith requires parties to apply the law of their state.
C:It is a treaty.
D:The principle of Freedom to Contract allows the parties to choose the law that governs their international contracts