A diagram is drawn showing a swing set with a swing pulled backward prior to release. The diagram shows how the swing will move forward and then backward after it is initially released. At which point in the diagram is all of the energy gravitational potential energy?

a
at the highest point as the swing is moving forward
b
when the swing is pulled back prior to release
c
Just after the swing is released
d
as the released swing begins moving backward

a, at the highest point as the swing is moving forward.