I think the answers are A and B, because: QoS mechanisms for Video- In principle, the QoS mechanisms used to deliver the SLAs for a video transport network are mostly the same as those for audio. There are some differences though, mostly because of the bursty nature of video and VBR (variable-bit-rate) transmission.

Selected Answer: AB L2 bandwidth Unlike voice, real-time IP video traffic in general is a somewhat bursty, variable bit rate stream. https://www.cisco.com/c/en/us/support/docs/quality-of-service-qos/qos-video/212134-Video-Quality-of-Service-QOS-Tutorial.html

Selected Answer: A I go with A and B

Selected Answer: AC I would say A and C, because if we have a bursty behavior it means we have some congestion on our network so we need QoS. The answer B is a fact, it's not up to a network. The answer C is correct if we have a poor link we will have a traffic to priorize. So A and C

Selected Answer: AB Re-reading the link from DaKenjee, I vote A and B. Even though C is correct, I think A and B are the better answers. Usually Cisco is looking for a more generic answer, not something specific to a particular link with underprovisioned bandwidth. Just going with my gut, from experience taking dozens of Cisco exams.

Selected Answer: AB The correct answers are definitely A and B. "Provisioned bandwidth of the link" is a result, not a technical reason for implementing QoS.

Selected Answer: AB When setting region settings for audio in the Cisco Unified Communications Manager, the administrator only needs to choose the compression type and audio codec preference. Audio media is very predictable, so the bandwidth used is based directly on the codec selection. However, video is very greedy and bursty when it comes to bandwidth consumption. Video codecs do not have a fixed bandwidth rate like audio codecs. A video call can be placed using 480p30 resolution at 384 kbps or at 2 Mbps. CCNP and CCIE Collaboration Core CLCOR 350-801 Official Cert Guide Chapter 15: Cisco Unified Communications Manager Setup