Why can the volume of a sample of plasma change when the substance is moved from one container to another?

A Plasma is made of charged ions and electrons, so they interact differently in different places.
B Plasma can have lots of space between its particles, so it naturally expands and compresses.
C Plasma is made of neutral atoms that can split into separate ions and electrons when placed in a new container.
D Plasma can change between a rigid shape and a free-moving form, so it will have different volumes in different containers.