Explanation
The physical security of crypto keys is of some concern, but guards or vaults are not always necessary.
Two-person integrity might be a good practice for protecting keys. The best answer to this question is option A, because it is always true, whereas the remaining options depend on circumstances.

Explanation/Reference:
Explanation:
AES is an encryption standard. Link encryption is a method for protecting communications traffic. One-time pads are an encryption method.

Explanation
Volume storage is allocated via a LUN to a system and then treated the same as any traditional storage. The operating system is responsible for formatting and securing volume storage as well as controlling all access to it. Applications, although they may use volume storage and have permissions to write to it, are not responsible for its formatting and security. Both a hypervisor and the management plane are outside of an individual system and are not responsible for managing the files and storage within that system.