A branch office of Acme Insurance has 15 IP phones connected to the main office using the distributed call processing model. Normally， the phones work with great quality. However， during very busy times when all of the agents are on the phone at the same time， the voice quality drops precipitously. Words or phrases or both are dropped from conversations. What is the most likely cause of the problem？（）
- Alarge files are being downloaded over the WAN network
- BIP phone traffic is not being classified correctly
- Cmore bandwidth is required for the office LAN
- DCall Admission Control has not been implemented
- Eemployees are watching videos over the internet
- Fheader compression is not being used