希望对Add方法能够被客户端远程调用，下列关于服务协定设计正确的是（）

A.[ServiceContract]public Class Service1{[Operation Contract]double Add（double n1，double n2）}
B.[ServiceContract]public Interface IService1{[Operation Contract]double Add（double n1，double n2）}
C.[ServiceContract]public Interface IService1{double Add（double n1，double n2）}
D.public Interface IService1{[Operation Contract]double Add（double n1，double n2）}