Considering only the initial and final situations, identify which mechanical energies have changed. In addition, determine whether you will need to consider any work done by external forces or changes in thermal energy.

Check all that apply.
A) Kinetic energy has changed.
B) Gravitational potential energy has changed.
C) Spring potential energy has changed.
D) Work by external forces on the system must be considered.
E) Thermal energy of the system has changed.