Both classes and interfaces represent a grouping of functionality and, therefore, both can be used to define a WCF service contract. However, it is recommended that you use interfaces because they directly model service contracts. Without an implementation, interfaces do no more than define a grouping of methods with certain signatures. Which of the following is a benefit of using interfaces to define Service Contracts?
A.	Service contract interfaces can extend any number of other service contract interfaces.
B.	You can modify the implementation of a service contract by changing the interface implementation, while the service contract remains the same
C.	A single class can implement any number of service contracts by implementing those service contract interfaces.
D.	All of these
Answer:D
Both classes and interfaces represent a grouping of functionality and, therefore, both can be used to define a WCF service contract. However, it is recommended that you use interfaces because they directly model service contracts. Without an implementation, interfaces do no more than define a grouping of methods with certain signatures. Which of the following is a benefit of using interfaces to define Service Contracts?
A.	Service contract interfaces can extend any number of other service contract interfaces. B.	You can modify the implementation of a service contract by changing the interface implementation, while the service contract remains the same C.	A single class can implement any number of service contracts by implementing those service contract interfaces. D.	All of these