Why do liquids and gases take the shape of their containers while solids do not?

Solid does not take up the container because its whole. A liquid is wet and shapes the container.

Liquids can flow because their particles can move over each other. When water is poured into a glass, the particles of water move over each other and into the corners of the glass. The particles keep on moving over each other as the water takes the shape of the glass. Gases can flow because they can move in any direction.