Explanation/Reference:
Confidentiality ensures that a message can only be read by the intended recipient. Encrypting a message provides confidentiality.
Different steps and algorithms provide different types of security services:
A message can be encrypted, which provides confidentiality.

A message can be hashed, which provides integrity

A message can be digitally signed, which provides authentication, nonrepudiation, and integrity.

A message can be encrypted and digitally signed, which provides confidentiality, authentication,

nonrepudiation, and integrity
Incorrect Answers:
B: A digital signature is required to provide non-repudiation for a message. Encryption alone does not provide non-repudiation.
C: A digital signature is required to provide authentication for a message. Encryption alone does not provide authentication.
D: A hash is required to provide integrity for a message. Encryption alone does not provide integrity.
References:
Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, 2013, pp. 829-830