The correct option is
D) can be transformed to different voltages
In fact, transformers can be used in order to change the voltage of an alternating current. This feature is particularly useful, because it allows to transmit electricity through power lines using very high voltages, and this allows to reduce the power dissipated along the lines.
In fact, the power generated by a power station is the product between the current and the voltage:
[tex]P_{in}= VI[/tex]
So the current is:
[tex]I= \frac{P_{in}}{V} [/tex] (1)
The power dissipated along the transmission line, instead, is given by
[tex]P_{diss} = I^2 R[/tex]
and if we use (1) inside this, we find
[tex]P_{diss} = \frac{P_{in}^2}{V^2} R[/tex]
so we see that the higher the voltage, the lower the power dissipated along the transmission lines.
Then, transformers are also used at the end of the power lines, in order to convert these very high voltages into the standard voltage (e.g. 240 V) used by household appliances.
