AWS Certified Foundational CLF-C02 Book

An access key is a pair of long-term credentials that consists of an access key ID and a secret access key. An access key is used to sign programmatic requests to the AWS CLI or AWS API (directly or using the AWS SDK). An access key allows a user to access the AWS account through a CLI, which is a tool that enables users to interact with AWS services using commands in a terminal or a script12.

The other options are not correct, because:

To access the AWS account as the AWS account root user, a user needs the email address and password associated with the account. The root user has complete access to all AWS resources and services in the account. However, it is not recommended to use the root user for everyday tasks3.

To access the AWS account through the AWS Management Console, a user needs a user name and password. The console is a web-based interface that allows users to manage their AWS resources and services using a graphical user interface4.

To access all of a company’s AWS accounts, a user needs to use AWS Organizations, which is a service that enables users to centrally manage and govern multiple AWS accounts. AWS Organizations allows users to create groups of accounts and apply policies to them5.

References:

Managing access keys for IAM users - AWS Identity and Access Management

What Is the AWS Command Line Interface? - AWS Command Line Interface

AWS account root user - AWS Identity and Access Management

What Is the AWS Management Console? - AWS Management Console

What Is AWS Organizations? - AWS Organizations

Amazon EC2 is the AWS service that the company should use to meet its requirements of retaining full control of patch management for the guest operating systems that host its applications. Amazon EC2 is a service that provides secure, resizable compute capacity in the cloud. Users can launch virtual servers, called instances, that run various operating systems, such as Linux, Windows, macOS, and more. Users have full administrative access to their instances and can install and configure any software, including patches and updates, on their instances. Users are responsible for managing the security and maintenance of their instances, including patching the guest operating system and applications. Users can also use AWS Systems Manager to automate and simplify the patching process for their EC2 instances. AWS Systems Manager is a service that helps users manage their AWS and on-premises resources at scale. Users can use AWS Systems Manager Patch Manager to scan their instances for missing patches, define patch baselines and maintenance windows, and apply patches automatically or manually across their instances. Users can also use AWS Systems Manager to monitor the patch compliance status and patching history of their instances. References: What is Amazon EC2?, AWS Systems Manager Patch Manager

AWS CloudHSM provides hardware-based key management to manage and protect encryption keys in the AWS Cloud. It allows customers to generate and use their own encryption keys while complying with rigorous security requirements. While AWS Certificate Manager (ACM) manages SSL/TLS certificates, it does not handle encryption keys independently, and AWS License Manager and AWS Directory Service are not designed for managing encryption keys. AWS KMS is also relevant for key management but wasn't listed as an option in this question.

Availability Zones are components of AWS infrastructure that can help the company ensure that the application is highly resilient. Availability Zones are multiple, isolated locations within each AWS Region. Each Availability Zone has independent power, cooling, and physical security, and is connected to the other Availability Zones in the same Region via low-latency, high-throughput, and highly redundant networking. Availability Zones allow you to operate production applications and databases that are more highly available, fault tolerant, and scalable than would be possible from a single data center.