An important principle in information security is the concept of layers of security, which is often referred to as layered security, or defense in depth. Which of the following is not an example of a layer of security?

a. a firewall
b. a server
c. an application
d. a control
e. standard

e) Standard

Explanation:

Information security simply means the act of preventing unauthorized access, use, disruption, modification or disclosure of information.

Layered security is the practice of combining mitigating security controls to guide and protect resources, data or device

Dfinitions of the options given

1. Firewall: This is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules. A firewall typically establishes a barrier between a trusted internal network and untrusted external network for example, the Internet

2. A server: A server is a type of computer or device on a network that manages network resources.

3. An application:  An application is a program or group of programs designed for end users. There are some applications that can serve as securities. For example: Antivirus

4. A control: A control is defined as the ability to manage, organize, or run something on a computer. In user control, you will have to set up a password to protect your computer.

5. A standard: A standard is a set of specifications for hardware or software, agreed upon by academic and industry contributors. Common examples of standards include multiple IEEE standards for electrical interfaces (computer cables),

From the above explanation, all are example of a layer of security except standard which cannot protect or serve as a security.  

i'm so sorry that's not a question and this isn't an answer