This is because Best Effort traffic is all other kinds of non-detrimental traffic that are not sensitive to Quality of Service metrics (jitter, packet loss, latency). A typical example would be peer-to-peer and email applications2. Background traffic is a type of traffic that is used for system maintenance or backup purposes and does not affect the performance or availability of the network3.
Therefore, Best Effort traffic has a higher priority than Background traffic in terms of network resources allocation and management.
1: https://www.arubanetworks.com/techdocs/ArubaDocPortal/content/docportal.htm 2:
https://stackoverflow.com/questions/33854306/best-effort-traffic-and-real-time-traffic-difference 3:
https://www.informit.com/articles/article.aspx?p=25315&seqNum=4

Explanation
These are the correct statements about access from the servers to the Core when the ISL link between the switches fails, but the keepalive interface functions. Server 1 can access the core layer via both uplinks because it is connected to VSX-A, which is still active for VLAN 10. Server 2 can also access the core layer via its uplink to VSX-B, which is still active for VLAN 10 because of Active Gateway feature. Server 1 and Server 2 can communicate with each other via the core layer because they are in the same VLAN and subnet, and their traffic can be routed through the core switches. The other statements are incorrect because they either describe scenarios that are not possible or not relevant to the question. References:
https://www.arubanetworks.com/techdocs/AOS-CX/10.04/HTML/5200-6728/bk01-

Explanation
These are the correct statements regarding the ERSPAN session that needs to be established on an AOS-CX switch for a network administrator to examine the packets over a period of time from their desktop. ERSPAN (Encapsulated Remote Switched Port Analyzer) is a feature that allows an AOS-CX switch to mirror traffic from one or more source ports or VLANs to a remote destination IP address over a GRE (Generic Routing Encapsulation) tunnel. The destination IP address must be the IP address of the administrator's desktop, which must have a packet capture tool installed to receive and analyze the mirrored traffic. The encapsulation protocol used for ERSPAN is GRE, which adds a header to the mirrored packets with information such as source and destination IP addresses, session ID, etc. The other statements are incorrect because they either do not specify the correct destination IP address or do not use ERSPAN or GRE. References:
https://www.arubanetworks.com/techdocs/AOS-CX/10.04/HTML/5200-6728/bk01-ch02.html
https://www.arubanetworks.com/techdocs/AOS-CX/10.04/HTML/5200-6728/bk01-ch03.html