Comprehensive and Detailed Explanation From Exact Extract:
Non-repudiation ensures that a sender cannot deny sending a message. Digital signatures provide non- repudiation because they use the sender's private key, which only the legitimate owner possesses. When the email recipient verifies the digital signature using the sender's public key, it proves the email was sent by the true owner of the private key and has not been altered.
Confidentiality (B) ensures information is protected from unauthorized access and is usually achieved through encryption. Integrity (C) ensures data has not been modified, while authentication (D) verifies the identity of a user. Although digital signatures also support integrity and authentication, the specific property that prevents denial of sending the email is non-repudiation.
Security+ SY0-701 highlights digital signatures as a cryptographic mechanism used for authentication, integrity, and non-repudiation, especially in email security, PKI systems, and secure messaging.
Thus, the correct answer is Non-repudiation.

A host-based firewall controls incoming and outgoing network traffic on a device by enforcing security rules, effectively blocking unwanted or insecure communications. It is specifically designed to protect the device from unauthorized access and malicious traffic.
System hardening (A) reduces vulnerabilities by disabling unnecessary services and patching but does not control communications dynamically. Intrusion detection systems (C) detect suspicious traffic but typically do not block it (unless paired with prevention). Anti-malware (D) protects against malicious software but not directly network communication filtering.
Host-based firewalls are a fundamental component of endpoint security highlighted in the Security Operations domain of SY0-701#6:Chapter 11 CompTIA Security+ Study Guide#.

A regulatory requirement is a mandate imposed by a government or an authority that must be followed by an organization or an individual. In a banking environment, audits are often required by regulators to ensure compliance with laws, standards, and policies related to security, privacy, and financial reporting. Audits help to identify and correct any gaps or weaknesses in the security posture and the internal controls of the organization.
Reference:
Official CompTIA Security+ Study Guide (SY0-701), page 507
Security+ (Plus) Certification | CompTIA IT Certifications 2

Full disk encryption (FDE) is a technique that encrypts all the data on a hard drive, including the operating system, applications, and files. FDE protects the data from unauthorized access in case the laptop is lost, stolen, or disposed of without proper sanitization. FDE requires the user to enter a password, a PIN, a smart card, or a biometric factor to unlock the drive and boot the system. FDE can be implemented by using software solutions, such as BitLocker, FileVault, or VeraCrypt, or by using hardware solutions, such as self-encrypting drives (SEDs) or Trusted Platform Modules (TPMs). FDE is a recommended encryption technique for laptops and other mobile devices that store sensitive data.
Partition encryption is a technique that encrypts only a specific partition or volume on a hard drive, leaving the rest of the drive unencrypted. Partition encryption is less secure than FDE, as it does not protect the entire drive and may leave traces of data on unencrypted areas. Partition encryption is also less convenient than FDE, as it requires the user to mount and unmount the encrypted partition manually.
Asymmetric encryption is a technique that uses a pair of keys, one public and one private, to encrypt and decrypt data. Asymmetric encryption is mainly used for securing communication, such as email, web, or VPN, rather than for encrypting data at rest. Asymmetric encryption is also slower and more computationally intensive than symmetric encryption, which is the type of encryption used by FDE and partition encryption.
Database encryption is a technique that encrypts data stored in a database, such as tables, columns, rows, or cells. Database encryption can be done at the application level, the database level, or the file system level. Database encryption is useful for protecting data from unauthorized access by database administrators, hackers, or malware, but it does not protect the data from physical theft or loss of the device that hosts the database.
Reference = Data Encryption - CompTIA Security+ SY0-401: 4.4, CompTIA Security+ Cheat Sheet and PDF | Zero To Mastery, CompTIA Security+ SY0-601 Certification Course - Cybr, Application Hardening - SY0-601 CompTIA Security+ : 3.2.