Under the AWS shared responsibility model, which of the following is the customer's responsibility?

The AWS shared responsibility model dictates that AWS is responsible for the security of the cloud, while the customer is responsible for security in the cloud. Application data security falls under the customer's responsibility, as they control the data, its classification, and how it's accessed and protected within their applications. AWS manages the underlying infrastructure, including the physical security of data centers, maintenance of underlying hardware for EC2 instances, and the maintenance of VPC components like network hardware and hypervisors. These are all part of the "security of the cloud" that AWS manages.