The functionalities of the presentation layer include:

Data Compression:
- The presentation layer is responsible for compressing data before it is transmitted over the network.
- Data compression reduces the size of the data, which leads to faster transmission and less bandwidth usage.
- This functionality is essential in scenarios where there is limited bandwidth or when large amounts of data need to be transferred efficiently.

Data Encryption:
- The presentation layer provides encryption and decryption services to ensure the security and confidentiality of data during transmission.
- Encryption transforms the data into an unreadable format using algorithms, making it difficult for unauthorized users to access or understand the information.
- Decryption reverses the encryption process, allowing the recipient to retrieve the original data.
- This functionality is crucial for sensitive information like passwords, personal data, financial transactions, etc.

Data Description:
- The presentation layer is responsible for transforming data into a standard format that can be understood by the receiving system.
- It provides a common language for different systems to communicate and interpret data correctly.
- Data description includes defining data structures, data types, and syntax rules to ensure interoperability between different platforms, operating systems, and applications.
- This functionality is essential in scenarios where data needs to be exchanged between heterogeneous systems.

All of the mentioned:
- The correct answer is option 'D' - all of the mentioned functionalities are included in the presentation layer.
- Data compression, data encryption, and data description are all key functionalities provided by the presentation layer to ensure efficient and secure data transmission.
- These functionalities work together to optimize data transfer, protect sensitive information, and enable communication between different systems.