When upgrading an existing operating system to a new version, what is the general rule regarding NOS files?

When upgrading an existing operating system to a new version, what is the general rule regarding NOS files?

A.
Newer versions of NOS files should be overwritten with older NOS file versions.

B.
Newer versions of NOS files should not be overwritten with older NOS file versions.

C.
Older NOS file versions should be used as far as possible.

D.
None of the above.

Explanation:
When upgrading an existing operating system to a new version, the general rule regarding NOS files is this: Newer versions of NOS files should be overwritten with older NOS file versions.
References:
Charles J. Brooks, Server+ Certification Exam Cram 2 (Exam SK0-002), QUE Publishing, Indianapolis, 2006, pp. 429-430.