Which of the following is an application layer service?*Network virtual terminalFile transfer, access, and managementMail serviceAll of the mentioned

To determine which of the options is an application layer service, we need to understand what the application layer is. The application layer is the topmost layer in the OSI model and is responsible for providing services directly to the end-user.

Now, let's analyze each option:

1. Network virtual terminal: This is not an application layer service. It is a software interface that allows a user to access and control a remote computer or network device.

2. File transfer, access, and management: This is an application layer service. It involves the transfer, access, and management of files between different systems or users.

3. Mail service: This is also an application layer service. It provides the ability to send, receive, and manage electronic mail messages.

Based on the analysis, the correct answer is "All of the mentioned" because both file transfer, access, and management, as well as mail service, are application layer services.