The correct answer is (d). A generator is a device that converts mechanical energy into electrical energy. It does this by using a rotating magnetic field to induce an electric current in a coil of wire. The current can then be used to power electrical devices.
A galvanometer is a device that measures electric current. It does this by using a magnetic field to deflect a needle. The amount of deflection is proportional to the amount of current.
A motor is a device that converts electrical energy into mechanical energy. It does this by using an electric current to create a magnetic field. The magnetic field then interacts with a permanent magnet to create a force that turns the motor.
An ammeter is a device that measures electric current. It does this by placing a small resistor in the circuit. The resistor creates a voltage drop that is proportional to the current. The ammeter measures this voltage drop and converts it into a reading of current.
I hope this helps!