6 mark question transformers & grid system

It says discuss the principles involved in high voltage transmission systems, explaining why a.c. is used in preference to d.c. and how the energy lost is minimised.
What I put was:
•To reduce energy lost you most reduce the resistance in the electric circuit as resistance loses energy from the electronic system as it is converted into thermal energy
•to reduce resistance in a wire you can do three things:
get a wire with a lower resistivity
increase the thickness of the wire
reduce the current flowing through it
•To reduce the current step up transformers are used, these increase the voltage but decrease the current.
•a.c. supply is more favoured as in a.c. the current is always fluctuating back and forth so most of the time the current is lower than it would with a d.c. supply.
•in transformers energy is conserved due to:
a soft iron core that can easily be magnetised and demagnetised due to the fluctuating current of the a.c. supply
an insulated core reduces the effect of eddy currents in the iron core thus no energy is lost due to the current flowing both ways
a low resistive winding

I realy hate these kind of questions, that and graphs

This looks OK.

You may also need to talk about efficiency.
In addition to using thick wire with low resitance to minmise heating effect of current you can also mention avoiding eddy currents by laminating core of a transformer. Also energy is lost magnetising and demagnetising the core so use magnetically soft core which can magnetise and demagnetise easily.
AC current also used to produce change in flux linkage which produces the emf in the secondary coil