The correct answer is: E. All of the above
A shunt is a low-resistance conductor that is connected in parallel with a measuring instrument to allow a larger current to flow through the instrument than would otherwise be possible. This increases the range of the instrument.
A multiplier is a device that is used to increase the voltage or current of a signal. This can be used to extend the range of an instrument by allowing it to measure higher voltages or currents than it would otherwise be able to.
A current transformer (CT) is a device that is used to measure current in a circuit. It does this by creating a magnetic field proportional to the current flowing through the primary winding. This magnetic field then induces a voltage in the secondary winding, which can be measured by an instrument.
A potential transformer (PT) is a device that is used to measure voltage in a circuit. It does this by creating a magnetic field proportional to the voltage applied to the primary winding. This magnetic field then induces a voltage in the secondary winding, which can be measured by an instrument.
All of these devices can be used to extend the range of instruments. The choice of device will depend on the type of instrument and the range that needs to be extended.