Which feature in Cisco WebEx is the most important differentiator compared to other vendor in the collaboration technology? Select exactly 1 answer(s) from the following:

A.
Cisco WebEx is always installed on- premises.

B.
With an account, everyone can join Cisco WebEx meetings.

C.
Cisco WebEx could be installed or collocated with Cisco Unified Communications Manager.

D.
Web conferencing service is delivered over a proprietary network, which is optimized for security, performance, and reliabiliy.