Which two statements about the DiffServ model are true？ （）
- A A class can be identified as a single application， multiple applications with similar service needs， or be based on the source or destination IP addresses.
- B A drawback of the DiffServ model is that it does not provide backward compatibility with devices that can only use the ToS field.
- C DiffServ uses the DiffServ field in the MAC header to mark frames into behavior aggregates （BAs）.
- D The DiffServ field occupies the same eight bits of the MAC header that were previously used for the ToS field.
- E The first six high-order bits of the DiffServ field are used to identify the Resource Reservation Protocol （RSVP） value.
- F The primary goal of DiffServ is scalability.