Updating the gateway on the web server to use 72.135.10.1 is the best action to take to resolve the issue of the web server being unavailable after being deployed in a public IaaS provider and assigned the public IP address of 72.135.10.100. Updating the gateway can ensure that the web server can communicate with the Internet and other networks by using the correct router or device that connects the web server's network to other networks. Updating the gateway can also improve performance and reliability, as it can avoid any routing errors or conflicts that may prevent the web server from responding to remote login requests. Reference: CompTIA Cloud+ Certification Exam Objectives, page 15, section 2.8

Renewing the expired certificate is what would most likely resolve the issue of users receiving a message indicating the connection is not secure when landing on a website that is hosted on a cloud platform and accessed through https://www.comptiasite.com. A certificate is a digital document that contains information such as identity, public key, expiration date, etc., that can be used to prove one's identity and establish secure communication over a network. A certificate can expire when it reaches its validity period and needs to be renewed or replaced. An expired certificate can cause users to receive a message indicating the connection is not secure by indicating that the website's identity or security cannot be verified or trusted. Renewing the expired certificate can resolve the issue by extending its validity period and restoring its identity or security verification or trust.

Peering is a type of network connection that allows two or more networks to exchange traffic directly without using an intermediary or a third-party service. Peering can help connect multiregions within an IaaS provider, as it can enable private networking in and between the multisites for data replication. Peering can also provide low latency, as it can reduce the number of hops and distance between the networks. Peering is the best solution for designing a multiregion network within an IaaS provider to support business requirements. Reference: CompTIA Cloud+ Certification Exam Objectives, page 15, section 2.8

Removing the lock from the two VMs is what would most likely enable the technician to delete the VMs that cannot be deleted due to an error. A lock is a feature that prevents certain actions or operations from being performed on a resource or service, such as deleting, modifying, moving, etc. A lock can help to protect a resource or service from accidental or unwanted changes or removals. Removing the lock from the two VMs can enable the technician to delete them by allowing the delete action or operation to be performed on them.

According to the CompTIA Cloud+ Study Guide1, autoscaling is "the ability to automatically increase or decrease the number of resources allocated to a cloud service based on the current demand". This means that autoscaling can help a cloud environment adjust to changes in traffic and workload, such as the ones caused by the new marketing promotions.
Ballooning, on the other hand, is "a technique used by hypervisors to reclaim unused memory from a virtual machine and allocate it to another virtual machine that needs more memory". This means that ballooning can help optimize the memory usage of a cloud environment, but it does not affect the number of resources allocated to a cloud service.
A firewall is "a device or software that monitors and controls the incoming and outgoing network traffic based on predefined rules". This means that a firewall can help protect a cloud environment from unauthorized access and malicious attacks, but it does not affect the number of resources allocated to a cloud service.
Switches are "devices that connect multiple devices on a network and forward data packets between them". This means that switches can help improve the network performance and connectivity of a cloud environment, but they do not affect the number of resources allocated to a cloud service.
Based on this information, I think the best answer to your question is D. Autoscaling. Autoscaling can help the company accommodate the new traffic by automatically increasing or decreasing the number of resources allocated to their web-application service based on the current demand. This can also help reduce costs and improve performance and availability.
I hope this helps you understand the concept of autoscaling better. If you want to learn more about CompTIA Cloud+, you can check out some of these resources:
CompTIA Cloud+ : Cloud High Availability & Scaling: A video course that covers the topics of high availability and scaling in cloud environments, including autoscaling, horizontal scaling, vertical scaling and cloud bursting.
Cloud+ (Plus) Certification | CompTIA IT Certifications: The official website of CompTIA Cloud+, where you can find exam details, preparation materials, renewal information and more.