The correct answer is C. raising an appropriate interrupt signal.
When a device needs to read or write data, it raises an interrupt signal. This signal is sent to the CPU, which then interrupts whatever it is currently doing and handles the read or write request.
Option A is incorrect because appending an extra bit of the address would not notify the system of a read or write operation. The system would need to know the address of the device that is being accessed in order to handle the request.
Option B is incorrect because enabling the read or write bits of the devices would not notify the system of a read or write operation. The system would need to know that the devices are enabled in order to handle the request.
Option D is incorrect because sending a special signal along the bus would not notify the system of a read or write operation. The system would need to know what the special signal means in order to handle the request.