Answer:
1. A solid has a definite shape that does not conform to the container shape.
2. A liquid has a definite shape that conforms to the container shape, but only to the extent of the liquid's volume; that is, a liquid takes the shape of an upper surface.
3. A gas has a indefinite (or amorphous) shape that does not conform to the container shape, but fills the entire shape and thus does not form an upper surface.