According to the Aruba Documentation Portal1, 802.1X is a standard for port-based network access control that uses a RADIUS server to authenticate and authorize wireless clients. 802.1X can be configured in different modes, such as bridge mode, tunnel mode, or split tunnel mode.
Option C: GRE tunnel
This is because option C shows how to configure an SSID in tunnel mode with the default AP-group settings on an Aruba switch. In tunnel mode, all client traffic from the access points is tunneled back to the controller and the controller would in turn put the client traffic onto the network2. The GRE protocol is used to encapsulate and decapsulate the traffic between the access points and the controller3.
Therefore, option C is correct.
1: https://www.arubanetworks.com/techdocs/AOS-CX/10.06/HTML/5200-7696/GUID-581D2976-694B-46C7-8497-F6B788AA05B2.html 2: https://community.arubanetworks.com/discussion/bridge-and-tunnel-mode 3: https://www.twingate.com/blog/ipsec-tunnel-mode

Wi-Fi 6 is an industry certification for products that support the new wireless standard 802.11ax, also known as "high-efficiency wireless". Wi-Fi 6 offers increased capacities, improved resource utilization and higher throughput speeds than previous standards.
Option B: ClientMatch
This is because option B shows how to use ClientMatch to optimize the wireless performance of Wi-Fi 6 clients on a UniFi network. ClientMatch is a feature that uses machine learning to analyze the traffic patterns of each client and assign them to the best available AP based on their location, device type, and network conditions2.
Therefore, option B is the best technology to implement for your customer's issue.
1: https://help.ui.com/hc/en-us/articles/221029967-UniFi-Network-Optimizing-Wireless-Connectivity 2: https://help.ui.com/hc/en-us/articles/360012947634-UniFi-Network-Optimizing-Wireless-Speeds

Explanation
According to the Aruba Documentation Portal1, 802.1X is a standard for port-based network access control that uses a RADIUS server to authenticate and authorize wireless clients. 802.1X can be configured in different modes, such as bridge mode, tunnel mode, or split tunnel mode.
Option C: GRE tunnel
This is because option C shows how to configure an SSID in tunnel mode with the default AP-group settings on an Aruba switch. In tunnel mode, all client traffic from the access points is tunneled back to the controller and the controller would in turn put the client traffic onto the network2. The GRE protocol is used to encapsulate and decapsulate the traffic between the access points and the controller3.
Therefore, option C is correct.
1:
https://www.arubanetworks.com/techdocs/AOS-CX/10.06/HTML/5200-7696/GUID-581D2976-694B-46C7-849
https://community.arubanetworks.com/discussion/bridge-and-tunnel-mode 3:
https://www.twingate.com/blog/ipsec-tunnel-mode

Strict queuing is the best scheduling technology to use for voice traffic on an AOS-CX switch.
Scheduling is a mechanism that determines how packets are transmitted from different queues on an egress port. Strict queuing is a scheduling method that gives the highest priority queue absolute preference over all other queues, regardless of their size or utilization. Voice traffic should be assigned to the highest priority queue and scheduled with strict queuing to ensure minimal latency and jitter. The other options are incorrect because they are either not scheduling methods or not optimal for voice traffic.

A session-based ACL is applied to traffic entering or leaving a port or VLAN based on the direction of the session initiation. To allow ping from any wired station to wireless clients but not vice versa, a session-based ACL should be used to deny icmp echo traffic from any source to any destination, and then permit icmp echo-reply traffic from any source to user destination. The user role represents wireless clients in AOS 10. Reference: https://techhub.hpe.com/eginfolib/Aruba/OS-CX_10.04/5200-6692/GUID-BD3E0A5F-FE4C-4B9B-BE1D-FE7D2B9F8C3A.html https://techhub.hpe.com/eginfolib/networking/docs/arubaos-switch/security/GUID-EA0A5B3C-FE4C-4B9B-BE1D-FE7D2B9F8C3A.html