According to the Virtual Machine Affinity and Anti-Affinity - VMware Docs1, affinity and anti-affinity rules allow you to spread a group of virtual machines across different ESXi hosts or keep a group of virtual machines on a particular ESXi host. An affinity rule places a group of virtual machines on a specific host so that you can easily audit the usage of those virtual machines.
Containers are "a standard unit of software that packages up code and all its dependencies so the application runs quickly and reliably from one computing environment to another" 2. Containers can run on any virtual machine or physical server, and they can be moved between different hosts without affecting the application functionality.
A firewall is "a device or software that monitors and controls the incoming and outgoing network traffic based on predefined rules" 3. A firewall can help protect a cloud environment from unauthorized access and malicious attacks, but it does not affect the placement of virtual machines on hosts.
Load balancers are "devices or software that distribute network or application traffic across a number of servers" . Load balancers can help improve the performance and availability of a cloud environment by distributing the workload among multiple servers, but they do not affect the placement of virtual machines on hosts.
Based on this information, I think the best answer to your question is C. Affinity rules. Affinity rules can help the pharmaceutical company ensure compliance by placing the application on its own virtual machine and keeping it on the same host. This way, the company can easily audit the usage of the application and avoid any changes in the hardware configuration.