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.

Adding a random string of characters, known as a "salt," to a password before hashing it is known as salting.
This technique strengthens passwords by ensuring that even if two users have the same password, their hashes will be different due to the unique salt, making it much harder for attackers to crack passwords using precomputed tables.References: CompTIA Security+ SY0-701 course content and official CompTIA study resources.

Air-gapping is the most effective way to protect an application server running unsupported software from network threats. By physically isolating the server from any network connection (no wired or wireless communication), it is protected from external cyber threats. While other options like port security or a screened subnet can provide some level of protection, an air gap offers the highest level of security by preventing any network-based attacks entirely.
References =
* CompTIA Security+ SY0-701 Course Content: Domain 03 Security Architecture.
* CompTIA Security+ SY0-601 Study Guide: Chapter on Secure System Design.

Ransomware-as-a-service is a type of cybercrime where hackers sell or rent ransomware tools or services to other criminals who use them to launch attacks and extort money from victims. This is a typical example of organized crime, which is a group of criminals who work together to conduct illegal activities for profit. Organized crime is different from other types of threat actors, such as insider threats, hacktivists, or nation-states, who may have different motives, methods, or targets. References: CompTIA Security+ Study Guide: Exam SY0-701, 9th Edition, page 17 1