A router (option C) is a network device that is used to separate broadcast domains. A broadcast domain is a logical division of a computer network in which all nodes can reach each other by broadcast at the data link layer. Routers operate at the network layer of the OSI model and use routing tables to determine the best path for forwarding packets between different networks.
By separating broadcast domains, routers can help to reduce network congestion and improve performance.
When a router receives a broadcast packet on one of its interfaces, it does not forward the packet to any other interfaces. This means that only devices within the same broadcast domain as the sender will receive the broadcast packet.

Explanation
The most likely cause of the failure is A. Thermal paste was not used.
Thermal paste, also known as thermal grease or thermal compound, is a substance that is applied between the CPU and the heat sink to improve the heat transfer and cooling of the CPU. Thermal paste fills the gaps and irregularities between the CPU and the heat sink, creating a better contact and reducing the thermal resistance .
According to some web search results , some signs and symptoms of not using thermal paste or using it incorrectly are:
*The CPU overheats and slows down or shuts down to prevent damage
*The CPU fan spins faster and louder to try to cool down the CPU
*The PC performance drops or becomes unstable
*The PC crashes or displays errors or blue screens
To fix this issue, the technician should apply thermal paste properly between the CPU and the heat sink, following these steps :
*Turn off the PC and unplug it from the power source
*Open the PC case and locate the CPU fan and heat sink
*Remove the CPU fan and heat sink from the motherboard
*Clean the surfaces of the CPU and heat sink with a lint-free cloth and alcohol
*Apply a small amount of thermal paste (about the size of a grain of rice) in the center of the CPU
*Reattach the heat sink and CPU fan to the motherboard, making sure they are aligned and secured
*Close the PC case and plug it back to the power source
The GPU needs additional power, the memory is insufficient, or the motherboard is incompatible are not likely causes of the failure, since they would not cause the PC to overheat and shut down after a few minutes. The GPU needs additional power if it has a high power consumption that exceeds the capacity of the power supply or the PCIe slot. The memory is insufficient if it cannot handle the applications or tasks that are running on the PC. The motherboard is incompatible if it does not support the CPU, RAM, or other components that are installed on it. These issues may cause poor performance, errors, or crashes, but not overheating and shutting down.

Explanation
The output from the cable tester indicates that there is an open fault in the cable, which means that one or more of the wires in the cable are not connected properly or are broken. The open fault affects the wires 3, 4, and 6, which are used for transmitting and receiving data in Ethernet networks. The open fault can cause network connectivity issues, such as no link, slow speed, or packet loss12.
To resolve this issue, the technician should use a crimper and a punchdown tool, which are tools that are used to attach connectors to cables or wires to patch panels. A crimper is a tool that squeezes or crimps a connector, such as an RJ-45, to the end of a cable, ensuring that the wires are securely inserted into the pins of the connector. A punchdown tool is a tool that pushes or punches a wire into a slot on a patch panel, creating a connection between the wire and the panel. Both tools can be used to fix or replace the faulty wires or connectors that cause the open fault12.
The other options are not as effective or relevant as a crimper and a punchdown tool. A loopback plug is a tool that is used to test the functionality of a network port or device, by sending and receiving signals from the same port or device. A loopback plug can help diagnose network problems, such as faulty ports or devices, but it cannot fix the open fault in the cable12. A network tap is a tool that is used to monitor or capture network traffic, by creating a copy of the data that passes through a network link. A network tap can help analyze network performance, security, or troubleshooting, but it cannot fix the open fault in the cable12. A toner probe is a tool that is used to trace or identify a cable or wire, by sending and detecting an audible tone along the cable or wire. A toner probe can help locate or label network cables or wires, but it cannot fix the open fault in the cable12. A Wi-Fi analyzer is a tool that is used to scan or measure wireless networks, by displaying information such as signal strength, channel, encryption, etc. A Wi-Fi analyzer can help optimize or troubleshoot wireless networks, but it cannot fix the open fault in the cable12.
References:
Network Tools - CompTIA A+ 220-1101 - Professor Messer IT ...
CompTIA A+ Core 1 (220-1101) Certification Study Guide, Chapter 5: Networking, Section 5.5:
Network Tools, Page 249
CompTIA A+ Core 1 (220-1101) and Core 2 (220-1102) Exam Cram, Chapter 5: Networking, Section
5.5: Network Tools, Page 213
CompTIA A+ Core 1 (220-1101) and Core 2 (220-1102) Pearson uCertify Course and Labs and Textbook Bundle, Chapter 5: Networking, Section 5.5: Network Tools, Page 250

The first step to troubleshoot a dim laptop display is to check the settings of the laptop display, such as the brightness level, the power plan, and the adaptive brightness feature. These settings can affect the brightness of the screen and can be adjusted by the user or by Windows automatically. If the settings are not optimal for the user's preference or environment, the screen may appear too dim even at full brightness. Therefore, the technician should check and modify these settings before trying other solutions.

Rapid elasticity is the ability of a cloud service to scale up or down the resources (such as virtual servers, storage, bandwidth, etc.) according to the demand of the users. This is an efficient way to handle unusually high web traffic usage, as it allows the company to provision more virtual servers when needed and release them when not needed, without wasting resources or paying for unused capacity. Rapid elasticity also improves the performance and availability of the web service, as it can adjust to the fluctuations in traffic and avoid overloading or downtime.
References
Rapid Elasticity in Cloud Computing: On-Demand Scaling for Business
Chapter 4: Virtualization and Cloud Computing