Which of the following statements best distinguishes the relationship between a service and a protocol in a layered network architecture?

1. ABoth services and protocols define the message formats and meanings used between the same layer entities, but at different abstraction levels.
2. BA service specifies what operations a layer offers to the layer above, whereas a protocol defines how peer entities within the same layer communicate to provide that service.
3. CA service is the physical implementation of a protocol; thus, changing the protocol automatically changes the provided service.
4. DA protocol defines the interface between two adjacent layers, while a service specifies the message exchange rules between peer entities.