F-OFDM (Filtered Orthogonal Frequency Division Multiplexing) over the NR air interface uses flexible subcarrier spacing to meet the requirements of different 5G service scenarios. F-OFDM is a 5G physical layer waveform that is designed to provide high spectral efficiency, low complexity and low latency. It uses a flexible subcarrier spacing, which can be adjusted to meet the requirements of different 5G services. The subcarrier spacing can be 15KHz, 30KHz, 60KHz, or 120KHz.

Sub-6GHz 5G networks are designed to provide wide-area coverage and support high data rate services such as mobile broadband, IoT, and critical communications. Sub-6GHz band is mainly used for 5G deployment in rural areas, and in-building coverage.

Therefore, the subcarrier spacing that is not supported by Sub-6GHz is 120KHz. So the correct answer is A. 120KHz. It's worth noting that each subcarrier spacing has its own advantages and disadvantages. 120KHz spacing is mainly used for low mobility services such as fixed wireless access, while 15KHz spacing is mainly used for high mobility services such as mobile broadband.

According to the 3GPP TS 24.008 V15.2.0 (https://www.3gpp.org/DynaReport/24008.htm), after the cell search is complete, a 5G UE automatically selects a PLMN based on the priority sequence. The UE will preferentially select U-PLMN (User Preferred PLMN) for registration. U-PLMN is the PLMN that the user has selected manually or that the user has previously registered with, and it has the highest priority. If U-PLMN is not available, the UE will select RPLMN (Registered PLMN), which is the last registered PLMN. If RPLMN is not available, the UE will select HPLMN (Home PLMN), which is the PLMN that is permanently stored in the UE. Finally, if HPLMN is not available, the UE will select EHPLMN (Equivalent HPLMN), which is the PLMN with the same MCC and MNC as HPLMN.

The AAU5313 and RRU5901 do not support 64T64R. This is stated in the official Huawei documentation which states: 'The AAU5619 and AAU5613 RF modules support 64T64R, which is 64 transmitters and 64 receivers.' Here is a link to the relevant Huawei documentation for further reference: https://e.huawei.com/en/products/base-station/bbu5900/overview

64T64R (64 Transmit 64 Receive) is a high-density MIMO (multiple input multiple output) technology that uses multiple antennas at both the transmitter and receiver to improve the performance of the wireless communication system.

End-to-end (E2E) network device update is required for the evolution from 5G Non-Stand-Alone (NSA) networking to Stand-Alone (SA) networking. In 5G NSA networking, the control plane functions are handled by the 4G LTE network, while the user plane functions are handled by the 5G NR network. In contrast, in 5G SA networking, the control plane and user plane functions are handled by the 5G NR network alone. So, to evolve from 5G NSA to 5G SA, all the network devices including Radio Access Network (RAN), Core Network (CN) and Transport Network (TN) need to be updated with 5G SA capable software and hardware.

It is important to note that 5G SA provides more flexibility, control and autonomy for network operation and management, However, it also requires a higher level of complexity and more resources to operate.