Below is a diagram of a weight on a spring. When the weight is pulled down and then released, the spring compresses and expands. Each position indicates a different point in time.

Which of the following statements is true?
a
In all four positions, mechanical energy is 0 J.
b
The elastic potential energy of the spring at Position 2 is converted to kinetic energy.
c
The chemical potential energy of the spring is greatest at Position 4.
d
In all four positions, the gravitational potential energy of the spring is the same.