Molecules in solids are packed a lot closer together than molecules in liquids and gases, so there is far less space between solid particles. Because of this, solid particles cannot move around quickly and freely like liquids and gases, instead they only vibrate so are fairly 'locked' into the same place, so solids have fixed volume and space.
The answer is C :
It controls the entry and exit of substances.
Answer:
both sugar and phosphate molecules
