Explanation:

When a device is granted access to the BUS, it means that the device is allowed to communicate with other devices connected to the BUS. The BUS is a shared communication pathway that allows multiple devices to transmit and receive data.

The statement "Once the BUS is granted to a device, it activates the BUS busy line" is correct because the BUS busy line is used to indicate that the BUS is currently being used by a device. When a device is granted access to the BUS, it activates the BUS busy line to signal other devices that it is currently using the BUS.

Benefits of BUS busy line activation:
- Prevents other devices from accessing the BUS simultaneously: By activating the BUS busy line, the device ensures that other devices do not attempt to access the BUS at the same time. This prevents data collisions and ensures a smooth data transmission process.
- Avoids conflicts and data corruption: If multiple devices attempt to access the BUS simultaneously, it can lead to conflicts and data corruption. By activating the BUS busy line, the device indicates that it has exclusive control over the BUS, reducing the chances of conflicts and data corruption.

Other options:
- The statement "Performs the required operation" is not necessarily true. Once granted access to the BUS, the device can perform its required operation, but it is not a direct consequence of the BUS being granted.
- The statement "Raises an interrupt" is not necessarily true. While a device may raise an interrupt in certain situations, it is not a direct consequence of the BUS being granted.
- The statement "All of the mentioned" is incorrect as not all the mentioned options are true.

Therefore, the correct answer is option 'A' - "It activates the BUS busy line."