What TankKuno said but also (And I don't know specifically the difficulty of Normanhurst and north Syd boys) The trials always attempt to be harder than the HSC is so if anything you'll hopefully be getting an even higher raw and scaled mark tomorrow :)
I think it works generally, but not for all functions.
I assume you're talking about dividing the x^2/2x^2 giving 1/2.
I think it's because no matter what other values of x you have lower than the highest degree, at bigger numbers something like an x^2 will be worth significantly more than even...
There is only one g(x) function which is the one on the top of the page. The g(0) we're looking at is the one in the top right.
while the answers are functions g(x). the x is not the same as it's replaced with f(x).
You can think about with just testing points.
Test x = a. f(a) = 0, therefore g(f(a)) = g(0), you can see that g(0) is a small positive number,
so it works with answer A and not B.