Your Customer has 21 users， each requiring both PC and IP Phone connectivity. Which is the correct configuration for this customer？（）
- A1 Cisco 2811 ISR,1 Catalyst Express 500G-12TC,2 Catalyst Express 500-24PC
- B1 Cisco 2851 ISR, Catalyst Express 500G-12TC,3 catalyst Express 500-24PC
- C1 Cisco 2821 ISR,Catalyst Express 500G-12TC,2 Catalyst Express 500-24PC
- D1 Cisco 2801 ISR,1 Catalyst Express 500-24PC