What is network virtualization?

Question $34$ options:

A$)$

combines networks by splitting the available bandwidth into independent channels that can be assigned in real time to a specific device

B$)$

combines the physical resources, such as servers, processors, and operating systems, from the applications

C$)$

combines multiple network storage devices so they appear to be a single storage device

D$)$

cffers backup services that use cloud resources to protect applications and data from disruption caused by disaster