Considers the assets of all things in an environment, and refers to the layering of security tools and methods often varying numerous parameters between layers, in an effort to restrict or prevent malicious users from penetrating anything more than the outer layers.
A. Protects assets in an information system environment by employing firewalls and information security policies.
B. Provides a roadmap for securing physical access points to a building as well as controlling the access to those points.
C. Guarantees protection of all layers in an information security architecture and infrastructure by employing multiple methods of protection between layers and across domains.

This question is incomplete, here is the complete question gotten from google:

Defense-in-depth is a strategy that: (choose best answer)

 a.  Considers the assets of all things in an environment, and refers to the layering of security tools and methods often varying numerous parameters between layers, in an effort to restrict or prevent malicious users from penetrating anything more than the outer layers.

  b. Protects assets in an information system environment by employing firewalls and information security policies.

 c.  Provides a roadmap for securing physical access points to a building as well as controlling the access to those points.

  d. Guarantees protection of all layers in an information security architecture and infrastructure by employing multiple methods of protection between layers and across domains.

Defense-in-depth is a strategy that  guarantees protection of all layers in an information security architecture and infrastructure by employing multiple methods of protection between layers and across domains - option C.

Explanation:

An approach to cybersecurity in whereby a series of defensive mechanisms are layered in order to protect valuable data and information is known as Defense in Depth (DiD) strategy .

In   DID, If one mechanism fails, another steps up immediately to obstruct an attack. This multi-layered approach with intentional redundancies increases the security of a system as a whole and addresses many different attack vectors.

Defense in Depth (DiD) strategy is only known for the description in option C, but it is not known for what is described in options A and B.

Thus, option C is the best answer

answervisible;