ANSWER:
The correct option is C: gas. When a gas is transferred from one container to another, its volume changes.
Step-by-step explanation:
The main reason is gases do not have a fixed volume. The volume of any gas depends on the container in which it is put. Gases have large inter-molecular spaces and can easily flow.
This is in contrast to liquids and solids that have a fixed volume. "Liquids" take the "shape of the container" but their volume doesn't depend on the container.