The correct answer is D. VPN.
A VPN (Virtual Private Network) is a service that allows a remote user to access network resources securely over the internet. A VPN creates an encrypted tunnel between the user's device and the VPN server, which acts as a gateway to the network. The user can then access the network resources as if they were directly connected to the network, without exposing their traffic to eavesdropping, interception, or censorship.
A VPN can provide remote users with access to various services on a company network, such as file and print services, client/server applications, and remote network administration1. A VPN can also protect the user's privacy and identity online by masking their IP address and location.
Reference:
* Remote Access to a Network - NETWORK ENCYCLOPEDIA, section "Remote access typically gives remote users access to the following services on a company network".

Two-factor authentication (2FA) significantly enhances security by requiring two forms of verification before granting access to company resources, making it harder for unauthorized users to gain access even if they have one of the credentials. PIN code enforcement adds an additional layer of security by ensuring that devices are protected by a PIN, making physical access to the device more challenging for unauthorized users. While the other options provide various benefits, 2FA and PIN code enforcement directly enhance the security of remote users accessing company resources.
Reference:
CompTIA A+ Core 1 Exam Objectives Section 2.7: Compare and contrast Internet connection types, network types, and their features.

An overheated CPU is the most likely cause of a computer that has been randomly shutting down without warning. A CPU generates heat when it performs calculations, and if the heat is not dissipated properly, it can damage the CPU or cause it to malfunction. A computer that shuts down randomly is a common symptom of an overheated CPU, as the system tries to protect itself from further damage by shutting down or restarting.
The other options are not as likely to cause this issue. A corrupted OS may cause the computer to crash, display errors, or fail to boot, but it does not affect the CPU temperature or the system fan. Incompatible memory modules may cause the computer to beep, display a blue screen, or fail to recognize the installed RAM, but they do not cause the CPU to overheat or the system to shut down randomly. Low system resources may cause the computer to slow down, freeze, or display a low memory warning, but they do not affect the CPU temperature or the system fan.
To troubleshoot and resolve an overheated CPU issue, the user should check and clean the air vents, provide proper ventilation, apply thermal paste, replace the fan or the heat sink, or upgrade the CPU if necessary. The user should also update the BIOS and the device drivers, adjust the power settings, and monitor the system temperature using diagnostic tools.
Reference:
CompTIA A+ Certification Exam Core 1 Objectives1
The Official CompTIA A+ Core 1 Student Guide (Exam 220-1101) eBook2
How to Troubleshoot Fan Issues | Dell US3
Why your laptop fan is loud and how to fix it | Asurion4
HP Notebook PCs - Fan is noisy and spins constantly (Windows)5

A spam gateway is a software solution that filters email messages based on various criteria, such as sender, recipient, subject, content, attachments, and URLs. A spam gateway categorizes incoming network messages as spam or non-spam, and either blocks, quarantines, or delivers them accordingly. A spam gateway can help protect email servers and users from malicious or unwanted emails, such as phishing, malware, or advertising.
A) Serves as a repository for email routing logs. This is not the primary function of a spam gateway. Email routing logs are records of the path and status of email messages as they travel through the network. Email routing logs can help troubleshoot email delivery issues, but they do not filter or categorize email messages.
B) Blocks unrequested ICMP packets from external networks. This is not the primary function of a spam gateway. ICMP (Internet Control Message Protocol) packets are used to communicate network information, such as errors, requests, or replies. Blocking unrequested ICMP packets from external networks can help prevent network scanning or denial-of-service attacks, but it does not filter or categorize email messages.
D) Mitigates DDoS attacks. This is not the primary function of a spam gateway. DDoS (Distributed Denial-of-Service) attacks are attempts to overwhelm a network or server with a large amount of traffic from multiple sources. Mitigating DDoS attacks can help maintain network availability and performance, but it does not filter or categorize email messages.