Introduction:
The option 'c) Telnet' allows a user at one site to establish a connection to another site and then pass keystrokes from the local host to the remote host. Telnet is a protocol that enables remote access to computers over a network. It provides a virtual terminal connection, allowing users to interact with remote systems as if they were directly connected.

Explanation:
Telnet is a client-server protocol that allows a user to establish a connection with a remote host and communicate with it using a terminal emulation application. Here's how it works:

1. Establishing a connection:
- The user initiates a Telnet session by running a Telnet client application on their local host.
- The user specifies the IP address or domain name of the remote host they want to connect to.
- The Telnet client establishes a connection to the Telnet server running on the remote host.

2. Passing keystrokes:
- Once the connection is established, the user can start passing keystrokes from their local host to the remote host.
- Any keystrokes entered by the user on their local host are sent over the network to the remote host.
- The remote host receives the keystrokes and processes them as if they were entered directly on the remote system.

3. Terminal emulation:
- Telnet provides terminal emulation, which means that the user's local terminal (or terminal emulator) behaves like the terminal on the remote host.
- The remote host sends output back to the user's local host, and it is displayed on the local terminal.
- This allows the user to interact with the remote system in a seamless manner, as if they were physically present at the remote location.

4. Usage:
- Telnet is often used for tasks such as remote administration, troubleshooting, and accessing resources on remote systems.
- It is commonly used for managing network devices, such as routers and switches, as well as accessing remote servers and mainframes.
- Telnet is a simple and widely supported protocol, but it lacks encryption and is considered insecure for transmitting sensitive information.