I don't see how B can be the answer:
Firstly GPE is always negative and approaches 0 as the distance approaches infinity, as shown in D.
Secondly the change in GPE should be greatest when the asteroid is close to the earth. B shows the asteroid having almost no change near earth and quickly approaching infinite GPE when it's far away, which makes no sense.
Have a talk to your teacher about it because it could just be a simple mistake on their part. For some example GPE graphs from the actual HSC which show the same shape as D have a look at:
27c of the 2014 paper
4 of the 2012 paper