Which best describes why a liquid needs a container when a solid does not?
solids fill their containers, and liquids have definite shapes.
solids have definite shapes, and liquids fill their containers.
solids particles do not expand to fill their containers, and liquid particles do.
solids particles expand to fill their containers, and liquid particles do not.

The answer is the second option: solids have definite shapes and liquied fill their containers. Liquid particles do not expand, they are just appart enough to permit a free limited movement which lets the liquid to take the form of the container. That is a common experience that you have daily, when you place water in a jar, the lquid will take the form of the jar, but in the cases of solid the particles are so tight that they conserve the form unless an external force deform the solid.