The correct answer is option 'D', which states that the Presentation layer is not a layer of the TCP/IP protocol.

Explanation:

The TCP/IP protocol is a suite of communication protocols used for connecting hosts on the internet. It is organized into four key layers, each responsible for specific functions.

1. Application layer:
The Application layer is the topmost layer in the TCP/IP model. It provides high-level protocols and services for user applications to interact with the network. It includes protocols such as HTTP, FTP, SMTP, DNS, etc., which enable functions like file transfer, email communication, web browsing, and more.

2. Transport layer:
The Transport layer ensures reliable and efficient data transfer between hosts. It is responsible for segmenting large chunks of data into smaller packets, ensuring their delivery, and managing flow control and error recovery. The most commonly used protocols at this layer are TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).

3. Internet layer:
The Internet layer is responsible for addressing, routing, and fragmentation of data packets. It uses Internet Protocol (IP) to provide logical addressing and routing between networks. IP ensures that packets are delivered to the correct destination by using unique IP addresses assigned to each device on the network.

4. Link layer:
The Link layer handles the physical connection between devices on the same network. It includes protocols for transmitting data over specific types of physical media, such as Ethernet, Wi-Fi, or DSL. This layer is responsible for packaging data into frames and delivering them between directly connected devices.

The Presentation layer, which is not part of the TCP/IP protocol, is a layer in the OSI (Open Systems Interconnection) model. It focuses on the formatting and presentation of data, including data encryption, compression, and protocol conversion. However, in the TCP/IP model, these functions are typically handled by the Application layer itself or by specific application protocols.

In summary, the TCP/IP protocol consists of the Application, Transport, Internet, and Link layers, while the Presentation layer is part of the OSI model and not directly associated with TCP/IP.