Final answer:
The model that shows compression is the one where a spring is compressed, which means work is done on the spring, storing potential energy.
Therefore, the correct choice is: a) Model A.
Step-by-step explanation:
The model that shows compression would typically be the one where there is a scenario involving the pressing or squeezing of materials into less space. In the given context, it seems that the description matches the process of compressing a spring. When you compress a spring by applying a force, you do work on the spring and store potential energy in it. The work done by a system, in this case, would be related to compression, which implies that an external force was applied to compress the spring and, thus, work was done by the system.
Therefore, the correct choice is: a) Model A.