If a company runs its databases on Amazon EC2 instances, which of the following is an AWS responsibility?

Operating system installations is an AWS responsibility under the shared responsibility model. When a customer uses Amazon EC2, AWS is responsible for the underlying infrastructure, including the virtualization layer and the physical servers, which encompasses installing the base operating system image on the EC2 instance. The customer is responsible for everything above the operating system, including database backups, database software patches, and operating system patches. These are all customer responsibilities because they involve managing the software and data running on the EC2 instance itself.