The correct answer is: All of the above.
Inductors, capacitors, and synchronous motors can all be used to compensate for voltage drop in power transmission lines.
Inductors store energy in a magnetic field, and when current flows through an inductor, it creates a magnetic field that opposes the change in current. This can be used to compensate for voltage drop by creating a counter-voltage that opposes the voltage drop.
Capacitors store energy in an electric field, and when current flows through a capacitor, it creates an electric field that opposes the change in current. This can also be used to compensate for voltage drop by creating a counter-voltage that opposes the voltage drop.
Synchronous motors are motors that have a rotating magnetic field that is synchronized with the electric field of the power line. This means that the motor can generate a counter-voltage that opposes the voltage drop.
In practice, a combination of inductors, capacitors, and synchronous motors is often used to compensate for voltage drop. This is because each type of device has its own advantages and disadvantages. For example, inductors are good at compensating for short-term voltage fluctuations, but they can cause problems with power quality if they are not properly designed. Capacitors are good at compensating for long-term voltage fluctuations, but they can cause problems with power factor if they are not properly designed. Synchronous motors are good at compensating for both short-term and long-term voltage fluctuations, but they are more expensive than inductors and capacitors.
The choice of which type of device to use depends on the specific application. For example, if the power line is subject to a lot of short-term voltage fluctuations, then inductors may be the best choice. If the power line is subject to a lot of long-term voltage fluctuations, then capacitors may be the best choice. If the power line is subject to both short-term and long-term voltage fluctuations, then synchronous motors may be the best choice.