The best tool to identify the correct cable is C. Toner probe.
A toner probe is a device that can be used to locate and trace a specific cable within a network rack or a wall outlet. A toner probe consists of two parts: a tone generator and a tone detector. The tone generator is connected to one end of the cable and sends an audible signal through the cable. The tone detector is used to scan the other end of the cable and pick up the signal. The tone detector emits a sound or a light when it detects the signal, indicating the correct cable.
A toner probe can be useful for network technicians who need to locate an end user's Cat 6 cable within a network rack that is poorly documented and has no cable management system. A Cat 6 cable is a type of twisted pair cable that can support high-speed data transmission over Ethernet networks. A network rack is a frame that holds network equipment, such as servers, switches, routers, or patch panels. A cable management system is a set of devices or methods that organize and secure the cables within a network rack .
The other options are not the best tools to identify the correct cable, because they have different purposes or limitations. A cable tester (option A) is a device that can be used to test the functionality and quality of a cable, such as its continuity, resistance, or interference. A cable tester can help diagnose and troubleshoot faulty cables, but it cannot locate or trace specific cables within a network rack. A network tap (option B) is a device that can be used to monitor and analyze the traffic and data that pass through a network. A network tap can help capture and inspect network packets, but it cannot locate or trace specific cables within a network rack. A loopback plug (option D) is a device that can be used to test the functionality and connectivity of a port or an interface. A loopback plug can help verify if a port or an interface is working properly, but it cannot locate or trace specific cables within a network rack.
For more information about toner probes and other network tools, you can refer to the following web search results: [What Is a Toner Probe?], [What Is Cat 6 Cable?], [What Is a Network Rack?], [What Is a Cable Tester?], [What Is a Network Tap?], [What Is a Loopback Plug?].

The next step that the technician should do to troubleshoot the issue is C. Swap the power supply if it is inoperable.
A power supply is a device that converts the alternating current (AC) from the wall outlet into direct current (DC) that the computer components can use. A power supply is essential for the computer to boot and function properly. A faulty or inadequate power supply can cause various issues, such as no power, no display, random shutdowns, or beeping sounds.
In this scenario, the technician is trying to fix a computer that fails to boot even when all the RAM is removed.
RAM stands for Random Access Memory, and it is a type of memory that stores data and instructions for the processor to access and process. RAM is also essential for the computer to boot and function properly. A faulty or incompatible RAM can cause various issues, such as no boot, no display, blue screen, or beeping sounds.
One of the basic troubleshooting techniques for a computer that fails to boot is to remove all the RAM modules and try to boot with one module at a time in different slots. This can help to identify if the problem is caused by a bad RAM module or a bad RAM slot. If the computer still fails to boot even when all the RAM is removed, it means that the problem is not related to the RAM, but to another component.
The next step that the technician should do is to swap the power supply if it is inoperable. This means that the technician should test the power supply with a multimeter or a power supply tester, and replace it with a known good one if it is faulty or insufficient. This can help to determine if the problem is caused by a bad power supply or a bad motherboard.
The other options are not the next steps that the technician should do, because they are less likely or less effective. Inspecting the motherboard for swollen capacitors (option A) may be helpful if the problem is caused by a damaged or defective motherboard, but it requires opening the computer case and visually examining the motherboard components. Replacing the CMOS battery (option B) may be necessary if the problem is caused by a low or dead CMOS battery, but it usually affects only the BIOS settings and not the boot process. Checking to see if the HDD power connectors are well seated (option D) may be useful if the problem is caused by a loose or faulty HDD connection, but it usually affects only the data access and not the boot process.
For more information about troubleshooting power supply and boot issues, you can refer to the following web search results: [How to Troubleshoot a Computer That Won't Turn On], [How to Test a Power Supply Using a Multimeter], [How to Fix a Computer That Shows No Sign of Power], [How to Troubleshoot Beep Codes].

The Official CompTIA A+ Core 1 and Core 2 Student Guide (Exams 220-1001 and 220-1002) | 193 Protected content. If you encounter an error that indicates unauthorized content or an HDCP error: * DVI, HDMI, DisplayPort, and Thunderbolt all provide support for the Digital Rights Management (DRM) mechanism High-bandwidth Digital Content Protection (HDCP). HDCP allows a content source (such as a Blu-ray disc) to disable itself if the display adapter and monitor and/or speaker system do not support HDCP and fail to authenticate themselves with the playback source. There have been various iterations of HDCP (at time of writing the current version is 2.2) and backward-compatibility can be problematic as authentication may fail between devices that support different versions of the standard.

A Virtual Private Network (VPN) is a secure method for connecting a remote user's laptop to a corporate server. VPNs use encryption to protect data transmitted over the internet.

A DNS record is a data entry in a DNS server that maps a domain name to a specific value, such as an IP address, a mail server, a name server, or a text string. There are different types of DNS records for different purposes, and each type has a specific format and syntax12.
The A record, also known as the address record, is the most common type of DNS record, and it is used to look up the IP address assigned to a domain name. The A record maps a domain name to an IPv4 address, which is a 32-bit numerical value that identifies a device on the internet. For example, the A record for www.google.com is 172.217.14.20612.
The other options are not correct because they are not used to look up the IP address assigned to a domain name. The MX record, also known as the mail exchange record, is used to specify the mail servers that handle the email for a domain name. The MX record maps a domain name to a priority value and a host name of a mail server. For example, the MX record for gmail.com is 10 alt1.gmail-smtp-in.l.google.com12.
The NS record, also known as the name server record, is used to delegate a domain name to a set of authoritative name servers. The NS record maps a domain name to a host name of a name server that can provide authoritative answers for the domain name and its subdomains. For example, the NS record for example.com is ns1.example.com12.
The SPF record, also known as the sender policy framework record, is used to prevent email spoofing and spamming by validating the sender's identity. The SPF record maps a domain name to a text string that specifies the authorized mail servers and IP addresses that can send email on behalf of the domain name. For example, the SPF record for microsoft.com is v=spf1 include:spf.protection.outlook.com -all12.
References:
* DNS Configuration - CompTIA A+ 220-1101 - 2.6
* CompTIA A+ Certification Core 1 (220-1101) [Video] - Packt Subscription, Section 2: Networking, Video 2.6: DNS Configuration
* CompTIA A+ Certification Core 1 (220-1101) - GitHub, Slide Handout PDFs 1101, Chapter 2:
Networking, Slide 2.6: DNS Configuration