Which of the following statements is true based on the propositions of the kinetic molecular theory?
1) Solids have definite shape and volume, and their particles are in a fixed non-vibrating position.
2) Liquids have indefinite shape and indefinite volume, so they can flow and be compressed.
3) Liquid substances have always had lower densities than solid substances.
4) Gases have low densities because of increased space between high-energy particles.